Isolated Chewtonian (Lower Ordovician) graptolites from western ...

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Isolated Chewtonian (Lower Ordovician) graptolites from western Newfoundland. Authors; Authors and affiliations. Jörg Maletz. Article. DOI : 10.1007/ ...
Pal~iontologische Zeitschrift

78 (1)

173-187

Stuttgart, April 2004

Isolated Chewtonian (Lower Ordovician) graptolites from western Newfoundland JORG MALETZ, B u f f a l o with 6 figures

Abstract: Isolated material of Chewtonian graptolites from the Cow Head Group of western Newfoundland shows some new and unexpected structural details. A high number of the two- and three-stiped Pendeograptus fruticosus specimens show metasicular origin for thl 1 combined with a normal isograptid proximal development. Sigmagraptine sicular development includes a large parallel-sided prosicula and a parallelsided metasicula. One species acquired an azygograptid-like proximal end, characterised by a loss of the initial branching, but kept the capacity to produce distal dichotomies. Maeandrograptus sinosus n. sp. and Keblograptus geminus n. sp. are described as new species.

Keywords: Ordovician, Chewtonian, graptolites, proximal development

Zusammenfassung: Unerwartete Strukturdetails konnten bei der chemischen Isolierung yon Graptolithenmaterial aus dem Chewtonium der Cow Head Gruppe (westliches Neufundland) gewonnen werden. Line Anzahl von zwei- und drei4istigen Pendeograptus fruticosus zeigen einen metasikularen Ursprung von thl t zusammen mit einer normalen Proximalentwicklung des isograptiden Typus. Die Proximalentwicklung der Sigmagraptinen beinhaltet eine groge Prosikula mit parallelen Seiten, sowie eine ebenso parallet-seitige Metasikula. Eine Art besitzt ein azygograptides Proximalteil ohne Proximalverzweigung, erh~ilt jedoch die Mrglichkeit yon distalen, dichotomen Verzweigungen. Maeandrograptus sinosus n. sp. und Keblograptus geminus n. sp. werden als neue Taxa beschrieben.

Schliisselwiirter: Ordovizium, Chewtonium, Graptolithen, Proximalentwicklung

Introduction Chewtonian graptolites are especially well known from a number of successions in Australasia (CAS & VANDENBERG 1988; VANDENBERG & COOPER 1992) and from the early Ordovician Cow Head Group of western Newfoundland (WILLIAMS & STEVENS 1988). Whereas the Australasian material usually is strongly tectonized, the preservation of the Newfoundland mate-

rial is excellent, even though most specimens are flattened. WILHAMS & STEVENS (1988), however, also described and figured a number of relief specimens, isolated from limestone lenses. B.-D. ERDTMANN (TU Berlin) provided the author with a number of shale samples, collected from the Martin Point south section (MPS) without exact documentation of the level of the material. Interestingly, WILLIAMS & STEVENS (1988: text-fig. 9) only indicated a single graptolitic level in the interval at MPS, bearing Didymograptellus bifidus and Xiphograptus svalbardensis (= Xiphograptus lofuensis herein). They documented a richer fauna from a single level in the Martin Point north section ( W I L L I A M S & STEVENS 1988: text-fig. 8). None of the faunas, however, matches the one here documented. Thus, the samples must have originated from a yet unrecorded level. Even though it might be impossible to figure out the exact horizon from which the material comes, enough information is available from the general succession in the Cow Head Group to pinpoint the biostratigraphic origin. The faunal association clearly indicates an age o f early Chewtonian. The base of the Chewtonian is defined by the FAD of Didymograptellus bifidus, a species not present in this collection, however. Still, the association of Pendeograptus fruticosus with a varied sigmagraptine fauna, and including Maeandrograptus sinosus n. sp., indicates a Chewtonian and not a late Bendigonian age. The samples were initially used for a trial to dissolve the shale and to get isolated graptolites for a taxonomic study. Surprisingly, the sample produced a rich graptolite fauna, as did later investigations of different shale units from both, the Cow Head and the Table Head Groups of western Newfoundland (MALETZ 1994, 1998; MALETZ & MITCHELL 1996; ALBANI et al. 2001). Even though all specimens are completely flattened, successful bleaching of the material yielded important information for a structural and taxonomic interpretation of individual species. A number of unexpected characters

Address of the author: Dr. Jrrg Maletz, Department of Geology, University at Buffalo, State University of New York (SUNY), 772 Natural Sciences and Mathematics Complex, Buffalo, New York 14260-3050, U.S.A.; e-mail 0 0 3 1 - 0 2 2 0 / 0 4 / 0 0 7 8 - 173

$ 3,75

© 2004 E. Schweizerbart'sche Verlagsbuchhandlung, D-70176 Stuttgart

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were discovered in the material that is worth a detailed description.

Material Isolated Chewtonian graptolites were first described in some detail from the Martin Point south section by WILLIAMS & STEVENS (1988) in their monograph on the Arenig faunas of the Cow Head Group, but only a few species were illustrated from isolated material. Numerous specimens of at least 16 species were recovered in the two samples dissolved with hydrofluoric acid. The material was carefully washed in distilled water and then either transferred to glycerine or mounted on glass slides in glycerine gelatine, a common method for the investigation of microfossil assemblages. All specimens are completely flattened. Bleaching with Schulze' solution rendered most of them transparent enough to study details of their rhabdosome and proximal development. The fauna includes: Pendeograptus fruticosus (J. HALL, 1858), Phyllograptus typus (J. HALL, 1865), Keblograptus geminus n. sp., Xiphograptus lofuensis (LEE, 1961), Didymograptellus? nitidus (J. HALL, 1858), Expansograptus grandis (MONSEN, 1937), Tetragraptus cf. spinosus (SPJELDNAES, 1953), Tetragraptus serra ssp., Tetragraptus cf. reclinatus (ELLES & WOOD, 1902), Goniograptus sp. (possibly two species), Maeandrograptus sinosus n. sp., Sigmagraptus praecursor RUEDEMANN, 1904, Sigmagraptine sp. 1-4. Repository: All figured specimens are kept in the type collection of the Geological Survey of Canada, Ottawa (GSC).

Systematic palaeontology The taxonomy follows BULMAN (1955, 1970), FORTEY & COOPER (1986), and WILLIAMS • STEVENS (1988). A detailed description is given only in cases of new information or newly discovered species. However, to depict a complete picture of the fauna, examples of all species from the two samples are figured.

pair. They are very similar to material described as Tetragraptus reclinatus by WILLIAMS & STEVENS (1988) from this interval (Fig. 2W). The most interesting form, however, might be a form identified preliminarily as Tetragraptus (?) sp. cf. T.(?) spinosus (SPJELDNAES, 1953) (Figs. 2S, V). It shows a comparatively small and slender sicula, 1.251.35 mm in length and 0.4-0.45 mm apertural width, with a rutellum, easily reaching 0.5 mm in length. The prosicula is 0.3 m m long and 0.2 mm wide at its aperture. Thl 1 originates from the lower part of the prosicula and is nearly symmetrically oriented to the sicula, a condition, found in the associated sigmagraptine Keblograptus. Also thl I bears a conspicuous rutellum. The proximal development is isograptid, dextral, with relatively slender crossing canals, but the further development is not shown in the juvenile specimens. The rhabdosome shape in larger specimens indicates that the species might be strongly reclined. A sigmagraptine relationship could be inferred from the rhabdosome characters and the species might not belong to Tetragraptus at all. Genus Pendeograptus BOUCEK & PRIBYL, 1953 Type species: Tetragraptus pendens ELLES, 1898.

Pendeograptusfruticosus (J. HALL, 1858) Figs. l A D , H, I; 2A-I, K, Q Description: The specimens show a long and slender sicula, between 1.9 and 2.35 mm in length and 0.5--0.6 mm wide at the aperture. A slight rutellum is invariably present in the specimens. The prosicula is 0.32-0.43 mm long and parallel-sided for most of its length. A number of longitudinal strengthening rods (L~ingsverstarkungsleisten: KRAFT 1927) are present. The number is difficult to ascertain, as the specimens are flattened and, thus, structures cover each other. All specimens show a short, distally broken nema, which may be thickened or bears a slender vane. Details of this structure are not available from the flattened specimens. The origin of thl 1 is between 0.35 and 0.75 mm below the apex of the

Order Graptoloidea LAPWORTH, 1875 Family Dichograptidae LAPWORTH, 1873 Subfamily Dichograptinae LAPWORTH, 1873 Genus Tetragraptus SALTER, 1863 Type species: Fucoides s e r r a BRONGNIART,1828. R e m a r k s : A number of possible tetragraptids are present in the collections, but none is well enough preserved to infer its exact structure or development. A form with a massive and up to 2.5 m m long sicula may be referred to Tetragraptus s e r r a (BRONGNIART, 1828) (Fig. 2J), but the specimens do not show more than the sicula and a partly developed thl 1. Other specimens are slightly less compact and show a complete first thecal

Fig. 1. - A--C, E, F, I: Pendeograptusfruticosus (J. HALL,1858); A, GSC 125727, juvenile with high metasicular origin of thl l; B. GSC 125728, specimen with relatively low metasicular origin of thl 1, obverse view, possibly two-stiped; C. GSC 125729,juvenile with high metasicular origin of th 11; E. GSC 125730,juvenile with high metasicular origin of thl 1; F. GSC 125731, juvenile with high metasicular origin of th 11; I. GSC 125735,juvenile with high metasicular origin of thl 1. _ D, G, H: Keblograptusgeminus n. sp.; D. GSC 125733, distorted proximal end; G. GSC 125732, proximal end; H. GSC 125734, holotype, largest specimen. Magnification ×27 for all specimens. An arrow indicates the prosicula/metasicula boundary and the origin of thl 1 in some specimens.

Isolated Chewtonian (Lower Ordovician) graptolites from western Newfoundland

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Isolated Chewtonian (Lower Ordovician) graptolites from western Newfoundland sicula. It is variably present in the lower part of the prosicula (Fig. 1I) or the upper part of the metasicula (Figs. 1B-D), as is well seen from bleached specimens showing the fusellar structure. Distal branching is present on stipe 1 in some specimens (Fig. 2K), but details are not well enough preserved to be sure about the exact branching style. It seems to be of the isograptid type. Most specimens in the collection are two-stiped morphs. Therefore they could be referred to Pendeograptus flagellifer (TrRNQUIST, 1901), according to MALETZ (1994a), a form common in the middle part of the TCyen Shale of Scandinavia. R e m a r k s : The proximal development type is isograptid dextral in all specimens and was described and figured in detail by WILLIAMS & STEVENS (1988) from isolated material, recovered from the D. bifidus Biozone at St. Paul's Inlet. However, all their material showed a prosicular origin of thl 1 COOPER d~; FORTEY (1983) suggested that the artus type proximal development in dichograptids is invariably related to a metasicular development. The here documented material, however, indicates that these two characters actually are independently distributed. Specimens with a prosicular and a metasicular origin are associated in the fauna, showing invariably an isograptid

Fig. 2. - A - I , K, Q: Pendeograptusfruticosus (J. HALL, 1858); A. GSC 125736, juvenile sicula and thl I with prosicular origin; B. GSC 125737, sicula with initial part of thl 1, originating from higher part of metasicula; C. GSC 125738, proximal end with prosicular origin of th 1 l; D. GSC 125731, proximal end with metasicular origin of thl I and thickened nema; E. GSC 125728, proximal end with metasicular origin of th 11 and thickened nema; F. GSC 125739, two-stiped specimen with prosicular origin of thl 1; G. GSC 125735, robust proximal end with prosicular origin of thl 1 and extremely wide crossing canal of thl2; H. GSC 125740, robust proximal end with prosicular origin of thl l; I. GSC 125741, juvenile with prosicular origin of th 11 and already thickened nema; K. GSC 125743, proximal end with low metasicular origin of thl ~ and possible branching on stipe one; Q. GSC 125747, two-stiped proximal end with prosicular origin of thl ~. J: Tetragraptus serra ssp.; GSC 125742, juvenile. - L---M, P, R, T, U: Didyrnograptellus nitidus (J. HALL, 1858); L - M . GSC 125744, juvenile in obverse and reverse view; P. GSC 125746, proximal end in reverse view; R. GSC 125748, proximal fragment in reverse view; T. GSC 125750, proximal end, reverse view; U. GSC 125751, proximal end, obverse view. - N-O: ?Expansograptus grandis (Monsen, 1937); GSC 125745, obverse and reverse view of juvenile. - S, V: Tetragraptus (?) cf. spinosus (SPJELDNAES, 1953); S. GSC 125749, juvenile in reverse view, showing nearly complete thl l; V. GSC 125752, slightly larger specimen. W: Tetragraptus cf. reclinatus (ELLES &;WOOD, 1902); GSC 125753, reverse view, largest s p e c i m e n . - Magnification x 15 for all specimens. The distance of 1 mm is indicated with two dots close to each specimen.

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proximal development. The variable origin of thl 1 is also remarkable as it is generally considered to be extremely consistent and populations including both, specimens with prosicular and metasicular origin of thl 1, have not been described before. BENSON 8,; KEBLE (1935), HARRIS & THOMAS (1938), THOMAS (1960) and VANDENBERG & COOPER (1992) documented a succession of four-stiped, threestiped and two-stiped P.fruticosus from Australia. This observation was not supported by COOPER ( 1 9 7 9 ) from New Zealand and WILLIAMS & STEVENS (1988) from western Newfoundland, however. The latter authors suggested that three-stiped P. fruticous may be a result of fragmentation. The specimens here described include two- and three-stiped specimens that are not based on fragmented material. Distribution: WILLIAMS & STEVENS (1988) recorded this species from the Tetragraptus approximatus to the lower part of

the D. bifidus biozones. Genus Xiphograptus COOPER & FORTEY, 1982 Type species: Didymograptusformosus BULMAN, 1936.

Xiphograptus lofuensis (LEE, 1961) Figs. 3I; 4C-H syn.: Didymograptus formosus svalbardensis ARCHER & FORTEY, 1974 R e m a r k s : Xiphograptus lofuensis is well known from isolated material (WILLIAMS & STEVENS 1988). Specimens are here illustrated for comparison with juveniles of Phyllograptus typus. Both species bear a dorsal virgella and juveniles are difficult to differentiate, even though the species are not thought to be closely related phylogenetically. The sicula of X. lofuensis is about 1.0-1.25 m m long and 0.4-0.45 m m wide at the aperture. The mature sicula bears a dorsal virgella of 0.6~).7 m m in length. The prosicula is 0.2-0.25 m m long and about 0 . 2 m m wide (Fig. 3I). The sicula of P. typus appears to slightly more slender (0.4 m m apertural width) and longer (1.25-1.4 mm). Differences are more pronounced in the shape of the prosicula. The prosicula of P. typus is considerably longer, and parallel-sided, compared to the more widening prosicula of X. lofuensis (compare Fig. 3C and Fig. 3I). Genus Didymograptellus COOPER & FORTEY, 1982 Type species: Graptolithus bifidus J. HALL, 1865. R e m a r k s : COOPER & FORTEY (1982) erected the genus to differentiate pendent didymograptids with prosicular origin of thl 1 and isograptid development from didymograptids with metasicular origin of thl 1 and artus type development. The genus was emended by MALETZ (1994) to include also phylogenetically related forms without the pendent rhabdosome shape.

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Isolated Chewtonian (Lower Ordovician) graptolites from western Newfoundland

Didymograptellus? nitidus (J. HALL, 1858) Figs. 2L, M, P, R, T, U

Description: The specimens show a compact sicula, 1.15-1.25 m m long without the rutellum and reaching an apertural width of 0.4-0.45 mm. The apertural part is slightly dorsally bent. The rutellum is a pronounced, about 0.2 m m long and wide spatulate process, especially conspicuous in juveniles (Figs. 2L, M, U). The prosicula is 0.2--0.25 mm long and shaped like a wide cone, nearly triangular. Its apertural width is about 0.2-0.25 mm. A short nema is invariably present, but does not reach more than 1 mm in all specimens. It apparently increases in length with the growth of the colony. The proximal end development is isograptid dextral with a symmetrical position of the two, initially slightly declined, stipes of the rhabdosome (Fig. 2R). The origin o f t h l 1 is about 0.2 mm below the apex of the prosicula, just above its aperture. It grows 0.3-0.35 m m down along the ventral side of the sicula, consistently expanding its width, before thl 2 originates in a dextral fashion. The protheca of th21 forms a 0.35-0.4 mm wide tube, crossing diagonally the sicula on the reverse side. It immediately gives birth to th21 left-handedly. The protheca of th21 is 0.18-0.22 mm wide initially. It forms a wide and rounded arch, while it slowly expands towards the aperture. The stipe width attains values between 0.85 and 0.9 m m across the apertures of the first thecal pair. Distal values are not available from the specimens. The isograptid suture between sicula and thl I below the isograptid arch is 0.2-0.25 mm long.

Remarks: All specimens are juveniles and proximal fragments and the shape of the mature colonies is uncertain. The identification of the species is based on the proximal end dimensions only, therefore. WILLIAMS & STEVENS (1988) discussed the dimensions and intraspe-

Fig. 3. - A-H, J: Phyllograptus typus J. HALL,1865; A, G. GSC 125754, juvenile sicula showing length of prosicula and origin of dorsal virgella; B. GSC 125755, sicula with initial part of thl 1, originating from lower part of prosicula, note developmentof dorsal virgella; C. GSC 125756, slightly older specimen with strongly widening thl 1; D. GSC 125757, specimen with nearly complete thl 1 bending outward, reverse view; E. GSC 125758, specimen with nearly complete thl 1 bending outwards, obverse view; F. GSC 125759,juvenile with strongly upturned growth of proximal thecae; H. GSC 125760, sicula with thl 1 approximately at the stage when thl 2 starts to differentiate; J. GSC 125762, juvenile with strongly upturned growth of proximal thecae, development not visible due to overlapping thecae in the flattened specimen. I: Xiphograptus lofuensis (LEE, 1961); GSC 125761, proximal end showing the size of the prosicula (arrowed). - L, N: Maeandrograptus sinosus n. sp.; L. GSC 125764; N. GSC 125766.- K, M: Sigmagraptine sp. 4; K. GSC 125763; M. GSC 125765.- NO: Sigmagraptine sp. 3; N. GSC 125767; O. GSC 125767.- P: Goniograptus sp. 1; GSC 125768. - Magnification x27 for all specimens. An arrow indicates the prosicula/metasicula boundary and the origin of thl I in some specimens.

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cific variation of D. nitidus in detail from numerous specimens. MALETZ (1994a) referred the species to Didymograptellus, based on the proximal end structure and the continued astogenetic stipe growth typical also for D. bifidus. WILLIAMS & STEVENS (1988: pl. 13 fig. 7) figured a single isolated proximal end they believed to be D. nitidus. The (incomplete) sicula is long and slender and might better be referred to a Tetragraptus specimen. Further isolated material of D. nitidus is unknown.

?Expansograptus grandis (MONSEN, 1937) Figs. 2N, O

Remarks: A few proximal ends of a horizontal didymograptid were encountered that are difficult to identify due to the lack of additional more mature growth stages. They show stout 1.4-1.5 m m long siculae with an apertural width of 0.5 mm and a short rutellum. The apertural part of the sicula is conspicuously bent dorsally. The prosicula appears to be wide and triangular shaped, about 0.28-0.3 mm long. A nema is not present in any of the specimens. The proximal end development is isograptid, dextral. The origin of thl 1 is in the lower part of the prosicula. It quickly expands and produces thl 2 about 0.4 mm below its apex. The crossing canal of th 12 is 0.45-0.5 mm wide. Crossing canal two originates at about 0.3 m m wide, and distinctly widens within the first 0.3 mm to a width of 0.5 mm. The quick expansion of thl 1, best seen in obverse view, is also characteristic for this species. In this respect it resembles the material described and figured by WILLIAMS & STEVENS (1988) as Didymograptus (Expansograptus) sirnilis and especially of Didymograptus (Expansograptus) abditus n. sp.? (WILLIAMS & STEVENS 1988: pl. 14 figs. 9--12). The material also shares the wide crossing canals and the considerably inclined sicula. WILLIAMS & STEVENS (1988: Text-fig. 12) illustrated the proximal development of E. similis, another similar species, from isolated material. They marked the origin of thl 2 to be close to the origin of thl 1, an interpretation that was obviously based on a pathological specimen (WILLIAMS • STEVENS, 1988: pl. 14 fig. 14) with damage to the initial growth o f t h l 1. All other isolated specimens show the origin from a wide foramen formed in the middle of thl 1. This is the development also shown in the here figured material. Subfamily Phyllograptinae LAPWORTH,1873 Genus Phyllograptus J. HALL, 1858 Type species: Phyttograptus typus J. HALL,1858.

Phyllograptus typus J. HALL, 1858 Figs. 3A-H, J; 4A-C

Description: Many growth stages o f P . typus are present in the material. As the specimens are all flattened, many

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important details, however, are not visible. The sicula is about 1.25-1.4 m m long and slender. It bears a nearly parallel-sided prosicula of 0.35-0.4 mm in length and 0.2~).25 mm in apertural width. The origin of the conspicuous dorsal virgella is about 0.1-0.15 mm below the prosicula-metasicula boundary (Fig. 3C). It starts as a rounded extension on the dorsal side of the sicula through deflection of the fuselli approaching each other on this side to form the zig-zag suture and quickly develops into a spiny structure after only a few fuselli are laid down. The rutellate stage of development in this material, thus, is strongly reduced already, different from the isolated material described by WILLIAMS & STEVENS (1988: pl. 24) from the D. bifidus Biozone of St. Paul's Inlet. The metasicula widens considerably from its apex and reaches a width of 0.4 ram. The origin of thl 1 is in the lower part of the prosicula, just above the boundary to the metasicula. The theca widens considerably on its downward path along the sicula and bends distinctly outwards and upwards close to the sicular aperture. The initial thecae are distinctly reclined aperturally (Fig. 3F), as is typical of all Phyllograptus (COOPER & FORTEY 1982). WILLIAMS & STEVENS (1988) described the formation of the virgella as differing from that of Xiphograptus by being hollowed and trough-shaped, similar to the rutetlum. In the material here investigated, the virgella is a true spine nearly from the beginning and does not differ in its formation from the virgella in Xiphograptus. FORTEY & COOPER (1986) used the presence of the virgella to define the Virgellina, in which Xiphograptus and Phyllograptus were regarded as ancestral to the biserial graptolites. WILLIAMS & STEVENS Remarks:

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(1988) questioned this relationship based on the quite different rhabdosome shapes and difficulties to explain transitions between both genera, a problem also encountered by MITCHELL (1990). MALETZ (1998a) indicated the presence o f Xiphograptus specimens in the Tetragraptus approximatus Biozone of the Cow Head Group, considerably below the first appearance of true Phyllograptus. This gives an indication of the independent origin of the dorsal virgella in Phyllograptus and Xiphograptus, as it predates Phyllograptus by a considerable time interval. If this is proven correct, the data support the origin of a virgella separately in at least three groups of early Ordovician graptolites, as the ventral virgella in the Diplograptoidea is now attributed to an origin through an isograptid ancestor (MITCHELLet al. 1995). Family Sinograptidae Mu, 1957 Subfamily Sigmagraptinae COOPER & FORTEY, 1982 Genus Maeandrograptus MOBERG, 1892 Type species: MaeandrograptusschmalenseeiMOBERG,1892. JAANUSSON(1964) and SKEVINGTON(1965) referred Didymograptus leptograptoides MONSEN, 1937 to the genus Maeandrograptus, instead of uniting this slender two-stiped form with Holmograptus, as was done by WILLIAMS & STEVENS (1988). Remarks:

Maeandrograptus sinosus n. sp. Figs. 3L, N; 5I-K, O D e r i v a t i o n o f n a m e : Referring to the long and slender thecae that are distinctly curved, producing a sinuous shape of the dorsal side of the stipes.

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F i g . 4. - A-C: Phyllograptus typus J. HALL,1865; A. GSC 125769,juvenile sicula showing length of prosicula and origin ofthl I; B. GSC 125770, sicula with incomplete th 11 originating from lower part of prosicula, note development of dorsal virgella; C. GSC 125771, all specimens in reverse view. - D-H: Xiphograptuslofuensis (LEE, 1961); D. GSC 125772; E. GSC 125773; F. GSC 125774; G. GSC 125775; H. GSC 125776, largest specimen. - Magnification ×17 for all specimens. The distance of 1 mm is indicated with two dots close to each specimen.

Isolated Chewtonian (Lower Ordovician) graptolites from western Newfoundland Type material: Several specimens, proximal ends and stipe fragments isolated from a shale sample from the Martin Point north section, D. bifidus Biozone. The specimen bear type numbers GSC 125764, 125766, 125783, 125787. GSC 125764 is the holotype (Figs. 3L; 5I).

Diagnosis: Horizontal to subhorizontal maeandrograprid with slender, strongly undulating stipes, no increasing thecal overlap distally, apertures with distinct ventrally curved rutellum and slight lateral lappets.

Description: The rhabdosome is slender, two-stiped with a slight asymmetry in the origination of the stipes. All recovered specimens are small and bear no more than five thecae. Thus, the final size of this conspicuous species is not known. The specimens appear to consist of thick periderm or bear strong cortical coverage and did not bleach readily. The sicula is 1.0-1.1 m m long and parallel-sided for most of the length. It bears a short rutellum at the aperture. The aperture is about 0.2 m m wide. The prosicular length is not recognized in the material. The origin of thl I is 0.45-0.5 m m below the apex of the sicula (Fig. 5I). It gives rise to thl 2 about 0.3 m m below its origin. At the same point thl 1 bends about 90 ° outwards to indicate the direction of stipe 1 growth. The proximal development is isograptid dextral, with a conspicuous asymmetry as stipe 1 originates higher than stipe 2. The crossing canal of thl 2 grows obliquely down across the reverse side of the sicula before it bends outwards to continue the stipe. Crossing canal 2 originates where crossing canal 1 crosses over, but initially grows horizontally towards the dorsal side of thl 1 to form stipe 1. The stipe width is about 0.4-0.45 m m in all specimens. This value is measured across the thecal apertures and includes the apertural denticle and the prothecal fold above the aperture. In between the thecal apertures the stipe width is closer to 0.25 mm. The stipes show a conspicuous undulation due to thecal bending, not the presence of true prothecal folds (Fig. 5J). The prothecae and metathecae bend into wide and rounded curves so that the apertures of the preceding thecae are buried in shallow excavations. The origins of each theca appear to be fairly wide and, thus, in part are responsible for the dorsal undulations of the stipes, but, the main structure is formed by the infolding of the thecal apertures. The stipe undulation is variable and may be less strongly expressed in the first thecal pair, but the single specimen differing from the general pattern seen in this species, may actually belong to Maeandrograptus leptograptoides (Fig. 50). The thecal apertures bear a conspicuous ventral denticle and slight lateral lappets, prominent in all species of Maeandrograptus. R e m a r k s : BULMAN (1950) first described material that might belong to this species from the Lower Ordovician of Tossfisen, Jemtland (central Sweden), but identified the species as Didymograptus callotheca. The material

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was later referred to Maeandrograptus cf. leptograptoides by SKEVtNGTON (1965). WILLIAMS • STEVENS (1988) described in detail the development of a different form they identified as Maeandrograptus cf. leptograptoides and illustrated the origin of thl 1 in the metasicula. This is, however, based on an assumption and needs to be confirmed, especially as the prosiculae in a number of sigmagraptines are relatively long and the origin of thl I appears low on the sicula (compare descriptions herein). The material of WILLIAMS & STEVENS (1988) is here considered conspecific with Maeandrograptus leptograptoides (MONSEN, 1937). Even if the prosicula is about 0.5 m m long, the origin of thl 1 could still be in the prosicula. In Holmograptus sp. A the prosicula, measuring about 0.35 m m , is extremely long and covers nearly half of the length of the complete sicuta (WILLIAMS & STEVENS 1988). WILLIAMS t~ STEVENS (1988: pl. 26 fig. 4) figured a fragment of an unidentified sigmagraptine fragment that shows thecal characters very similar to those of Maeandrograptus sinosus n. sp. It bears the same relationship between thecal apertures and dorsal bending of thecae, even though the fragment shows a larger open space for the thecal apertures and more slender prothecal tubes. There seems little doubt that this fragment may belong to a species of Maeandrograptus. A generally similar, but most probably not closely related species is the sinograptid Holmograptus serpens BRUSSA, 1999 from the Paraglossograptus tentaculatus Biozone of the Argentinian Precordillera Occidental. It bears a symmetrical development of the somewhat declined proximal end as all Holmograptus species do, combined with strongly sinuous thecal shapes. Both forms, thus, should not be confused.

Distribution: The exact distribution of Maeandrograptus sinosus n. sp. is unknown. The faunal association indicates a Chewtonian age for the Cow Head Material. BULMAN's (1950) material comes from the Tossfisen, Jemtland. The presence of this species on two palaeo-plates indicates a possible world-wide distribution and usefulness for biostratigraphic correlation. Genus Keblograptus RIVA, 1992 Type species: Didymograptus bidens KEBLE,1927.

Diagnosis (revised from RIVA 1992): Sigmagraptines with strongly widening thecal apertures and wide, triangular sicula; thecae show triangular shape with low overlap; sicula and th11 often, but not necessarily subsymmetrically to symmetrically arranged; thecal aperture may be reduced. R e m a r k s : The genus was established for pendent sigmagraptines with apertural infolds. It is here extended to include also forms without apertural infolds, but retaining the sigmagraptine proximal development and a subhorizontal to declined and pendent habit. A number of species show a strong reduction of the length of thl 1, re-

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suiting in a nearly s y m m e t r i c a l a r r a n g e m e n t . WILLIAMS & STEVENS (1988) d e s c r i b e d a n d figured a specimen identified as G r a p t o l o i d gen. A that bears a s y m m e t r i c a l d e v e l o p m e n t o f the p r o x i m a l e n d and a p p a r e n t l y very slender thecae with r e d u c e d a p e r t u r e size.

Keblograptus geminus n. sp. Figs. 1E-G; 5 A - H , L Derivation of name: Based on the proximal end symmetry of the sicula and thl 1: geminus (= latin for twin). Type material: Several specimens, proximal ends and stipe fragments isolated from a shale sample from the Martin Point north section, D. bifidus Biozone. The specimens bear type numbers GSC 125732-125734 and 125777-125782. GSC 125734 is the holotype (Figs. 1G; 5E).

Diagnosis: T w o - s t i p e d Keblograptus

with subhorizontal to d e c l i n e d r h a b d o s o m e and n e a r l y s y m m e t r i c a l l y d i s p l a y e d sicula and t h l 1.

D e s c r i p t i o n : The r h a b d o s o m e o f Keblograptus geminus n. sp. appears to be s u b h o r i z o n t a l to d e c l i n e d , but the material is too f r a g m e n t e d for a d e t a i l e d investigation o f its shape. A distal w i d e n i n g o f the stipes cannot be conf i r m e d from the stipe f r a g m e n t s , all s h o w i n g the same thecal apertural width. The sicula is 1.1-1.25 m m l o n g and widens conside r a b l y f r o m the apex. The p r o s i c u l a is 0 . 2 5 - 0 . 3 m m long and 0.2 m m wide at the aperture. T h e metasicula widens to 0 . 5 - 0 . 5 5 m m at the aperture. A strong rutellum is present and measures 0 . 3 - 0 . 3 5 m m in length. It is a widely r o u n d e d , s p o o n - s h a p e d structure. T h e sicula is nearly straight, but bends slightly d o r s a l l y at the aperture. T h e origin o f t h l i is 0 . 2 - 0 . 2 5 m m b e l o w the apex o f the sicula, just a b o v e the b o u n d a r y b e t w e e n prosicula and metasicula. T h l 1 widens q u i c k l y to a triangular shape with a width at the aperture o f about 0 . 6 5 - 0 . 7 ram. It is nearly s y m m e t r i c a l to the sicula in j u v e n i l e specimens. T h e p r o x i m a l d e v e l o p m e n t is isograptid dextral, with v e r y slender crossing canals. T h e s e are positioned h i g h l y a s y m m e t r i c a l l y . T h l 2 c r o s s i n g canal g r o w s obliquely d o w n w a r d s f r o m its origin about 0 . 3 - 0 . 3 5 m m b e l o w the origin o f t h l 1 and t o w a r d s the dorsal side o f the sicular aperture. C r o s s i n g canal 2 initially g r o w s upw a r d s f r o m its origin to the dorsal side o f t h l 1 and along it. Both crossing canals are 0 . 8 - 0 . 9 m m wide. T h e thecae are triangular in shape with a w i d e apertural o p e n i n g and slender, p a r a l l e l sided prothecae. T h e apertural width is 0 . 6 5 - 0 . 8 ram. The thecae are about 1.6-1.75 m m long and o v e r l a p for 0.3~3.4 mm. The s l e n d e r prothecae are about 0 . 8 - 0 . 9 m m long and o n l y 0 . 1 - 0 . 1 5 m m w i d e , b e f o r e the q u i c k l y e x p a n d to their apertures. 2 T R D m a y be e s t i m a t e d to 2 . 6 - 2 . 8 ram, but fragments usually s h o w o n l y o n e or two isolated thecae. L o n g e r stipe f r a g m e n t s h a v e not been found. R e m a r k s : WILLIAMS & STEVENS (1988) figured a single s p e c i m e n that m a y b e l o n g to this species, as Didymograptus? sp. from the D. bifidus B i o z o n e at Western

B r o o k Pont ( W B S 29). A further similar, this t i m e isolated, s p e c i m e n was illustrated as Didymograptus (s.1.)? sp. from St. Pauls Inlet (SPI 63, D. bifidus Biozone). It shows a m u c h w i d e r th21 than all specimens from the Martin Point collections and a s o m e w h a t different geometry. Keblograptus geminus n. sp. r e s e m b l e s Keblograptus mendicus KEBLE & HARRIS (WILLIAMS & STEVENS 1988) in shape and d e v e l o p m e n t , but differs in lacking the sinuous apertural m o d i f i c a t i o n s . It also shows a m u c h m o r e s y m m e t r i c a l d e v e l o p m e n t o f the sicula and t h l 1. G r a p t o l o i d gen. A (WILLIAMS & STEVENS 1988: pl. 24 fig. 15; pl. 30 fig. 1 1) also r e s e m b l e s Keblograptus geminus n. sp. in the shape o f the thecae and s y m m e try o f the p r o x i m a l end, but appears to possess a different distal thecal style. G e n u s Goniograptus M ' C o Y , 1876 Type species: Didymograpsus thureaui M'COY, 1876.

Goniograptus sp. Figs. 3P; 5M, N, P - T R e m a r k s : T h e m a t e r i a l consists o f a few s p e c i m e n s that m a y b e l o n g to m o r e than one species, b e c a u s e o f considerable differences in size and thecal shape. T h e y are included in Goniograptus b a s e d on the information and figures given by WILLIAMS • STEVENS (1988). D e t a i l e d p r o x i m a l end structure is not a v a i l a b l e from any other Goniograptus so far. A c c o r d i n g to the illustrations o f WILLIAMS & STEVENS (1988) the p r o x i m a l ends show a c o n s p i c u o u s d e v e l o p m e n t o f the r u t e l l u m on the sicula and consistently w i d e n i n g , d i c h o g r a p t i d thecae without a well d e v e l o p e d rutellum.

Fig. 5. - A - H , L: KebIograptus geminus n. sp.; A, B. GSC 125777,juvenile in obverse and reverse view; t2. GSC 125778, reverse view showing isograptid development with slender crossing canals, thickened nema; D. GSC 125779, juvenile showing origin ofthl I in lower part of prosicula; E. GSC 125734, holotype, proximal end in reverse view; F, G, H. GSC 125780, GSC 125781, GSC 125782, stipe fragments; L. GSC 125784, reverse view. I - K , O: Maeandrograptus sinosus n. sp.; I. GSC 125764, holotype, proximal end in reverse view; J, K. GSC 125766, GSC 125783, stipe fragments; O. GSC 125787, proximal end in reverse view. - N, Q--R: Goniograptus sp. 1; N. GSC 125786, proximal end in reverse view; Q. GSC 125768, reverse view; R. GSC 125789, reverse view. - M, P, S-T: Goniograptus sp. 2; M. GSC 125785, reverse view; P. GSC 125788, proximal end with one branching; S. GSC 125790, proximal end with one branching, reverse view; T. GSC 125791, juvenile in reverse view. - U-W: Sigmagraptus praecursor RUEDEMANN, 1904; U. GSC 125792, proximal end with lower part of sicula, showing several branching divisions; V. GSC 125793, incomplete proximal end; W. GSC 125794, incomplete proximal end, showing low origin of th 11. _ X-Y: Sigmagraptines indet.; X. GSC 125795, proximal end with sicula; Y. GSC 125796, proximal end with several branching divisions. - Magnification ×17 for all specimens. The distance of 1 mm is indicated with two dots close to each specimen.

Isolated Chewtonian (Lower Ordovician) graptolites from western Newfoundland

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183



184

JORGMALETZ

Species one (Figs. 3P; 5M, N, Q, R): The sicula is about 0.95 mm long without the rutellum, which measures 0.3 ram. The prosicula is 0.25 mm long and widens slightly towards its aperture reaching 0.18 mm in width. The aperture of the metasicula is 0.25 mm wide. The origin of thl 1 is in the lower part of the prosicula. The proximal development is isograptid dextral with a strong asymmetry of the proximal end. The specimen bears two complete thecae with an apertural width of 0.5-0.6 mm. Species two (Figs. 5P, S, T): The specimen bears a sicula of 1.4 mm in length provided with a 0.3 m m long, distinct rutellum. The prosicula is 0.25 mm long and 0.15 mm wide. The proximal development is isograptid dextral with an asymmetrical development typical of sigmagraptines. The apertural width of thl 2 and th21 is 0.5 mm. The thecae are more slender and longer than those of species 1. Stipe 1 shows a branching division with two incomplete thecae. The specimen is similar in dimensions and development to specimens referred to Goniograptus thureaui by WILLIAMS & STEVENS (1988: pl. 26 figs. 16, 17). Genus Sigmagraptus RUEDEMANN, 1904 Type species: Sigmagraptus praecursor RUEDEMANN,1904.

Sigmagraptus praecursor RUEDEMANN, 1904 Figs. 5U-W Description: The material is fairly poor and incomplete. A single proximal end fragment with an incomplete, 1.2 mm long sicula and a branching colony are referred to this species. The sicula appears to be very narrow and parallel-sided. The proximal fragment, in which a long part of the sicula is preserved, shows also a narrow and elongated initial part of thl 1 with a low, nearly symmetrical proximal development. The development is isograptid, dextral. It is well shown in a multiramous fragment, in which the lower part of the sicula is preserved only. The specimen displays the uni-lateral, monoprogressive branching typical of Sigmagrap-

tus. R e m a r k s : The material is fragmented, but the monoprogressive branching indicates its identity as Sigmagraptus. Isolated material described by WILLIAMS & STEVENS (1988) appears to be quite inhomogeneous and may belong to more than one species of sigmagraptine. Sigmagraptines indet. R e m a r k s : The following specimens are not assigned to a particular species, as details of the development of most sigmagraptines has not been described before and this isolated material cannot be compared in detail with any described shale specimen. Definitely a number of species can be differentiated based on dimensions of the prosicula, metasicula and the stipe development.

Sigmagraptine sp. 1 (Figs. 6A, C - F , I) Description: The rhabdosome is slender, possibly twostiped, horizontal or sub-horizontal. The sicula attains a length of 0.75-0.80 mm and is nearly parallel-sided. Only the prosicula widens slightly from its apex. It is 0.45--0.5 mm long and 0.2 m m wide at the aperture. The metasicula is parallel-sided and 0.2 mm wide aperturally, where it bears a slight rutellum. The proximal development is isograptid, dextral, with the typical sigmagraptine asymmetry. T h l 1 grows downwards along the sicula for about 0.25 m m before thl 2 originates and grows obliquely downwards to the dorsal side of the sicular aperture. Th21 initially grows upwards in an arch to the dorsal side of th 11 to form stipe one. The thecae are long and slender tubes with an inclination of less than 8°. They widen from initially 0.1 mm to apertural widths of 0.2-0.25 mm. The 2TRD is estimated to be around 1.9-2.2 ram. The thecal overlap is less than 0.2 mm. R e m a r k s : The species is characterised by a small sicula of which the prosicula amounts to about 50 %. The stipes are extremely slender and flexible. Branching has not been observed in the fragmented material, but may have been present. The species is similar to Sigmagraptine sp. 2, but differs in its dimensions and in a proportionally much larger prosicula. Sigmagraptine sp. 2 (Figs. 6B, H, J) Description: The known rhabdosome shape is twostiped, but only proximal fragments have been discovered. The complete sicula is 1.0-1.1 mm long and nearly

Fig. 6. - A, C-F, I: Sigmagraptine sp. 1; A. GSC 125797, proximal end, reverse view; C. GSC 125799, reverse view showing isograptid development with slender crossing canals, stipe broken on transfer; D. GSC 125800, stipe fragment, possibly belonging to this form; E. GSC 125801, proximal end in reverse view, note short free dorsal supra-apertural side of sicula; F. GSC 125802, reverse view; I. GSC 125804, specimen with long nema. - B, H, J: Sigmagraptine sp. 2; B. GSC 125798,juvenile in reverse view; H. GSC 125803, proximal end showing possible float; J. GSC 125805, completeproximal end in reverse view. - L--M, O-W, Y: Sigmagraptine sp. 3; L. GSC 125767, relatively wide stipe fragment possibly belonging to this species; M. GSC 125807, juvenile; O. GSC 125809, specimen with two complete thecae; P. GSC 125810, juvenile; Q. GSC 125811, juvenile; R. GSC 125812, juvenile with partially developed first theca; S. GSC 125813, juvenile; T. GSC 125814, juvenile showing complete first theca and origin of th2 in a distal position, no proximal dichotomy present; U. GSC 125815, small specimen with two complete thecae; W. GSC 125817, largest proximal end fragment with three complete thecae; Y. GSC 125819, specimen with six distal dichotomies,largest specimen. - G, K, N, V, X: Sigmagraptine sp. 4; G. GSC 125765, proximal end in reverse view; K. GSC 125806, proximal end with unbranched stipe one reaching four thecae; N. GSC 125808, proximal end; V. GSC 125816, incomplete proximal end; X. GSC 125818, proximal end with branching at th31. - Magnification ×17 for all specimens. The distance of 1 mm is indicated with two dots close to each specimen.

Isolated Chewtonian (Lower Ordovician) graptolites from western Newfoundland

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JORGMALETZ

p a r a l l e l - s i d e d . The p r o s i c u l a m e a s u r e s 0 . 3 8 - 0 . 4 mm. T h e m e t a s i c u l a is p a r a l l e l - s i d e d through its entire length. It bears a short r u t e l l u m o f 0.1 m m in length. The p r o x i m a l d e v e l o p m e n t is i s o g r a p t i d , dextral with a typical a s y m m e t r y . T h e c r o s s i n g c a n a l s are less than 0.1 m m w i d e . Distal b r a n c h i n g is u n k n o w n . T h e thecae are initially 0.1 m m w i d e and attain an apertural width o f 0 . 3 0.32 m m . T h e y o v e r l a p about 0.3 ram. The 2 T R D is not p o s s i b l e to m e a s u r e , as all m a t e r i a l consists on short f r a g m e n t s only. R e m a r k s : The species is s i m i l a r to S i g m a g r a p t i n e sp. 1, but differences in their d i m e n s i o n s s e e m to be consistent and i n t e r m e d i a t e s have not b e e n f o u n d in the material.

S i g m a g r a p t i n e sp. 3 (Figs. 6L, N , O - U , W , Y) D e s c r i p t i o n : T h e species a p p e a r s to be h i g h l y variable in its r h a b d o s o m e d e v e l o p m e n t . T h e r h a b d o s o m e varies f r o m a c o m m o n uni-stiped, b a s i c a l l y a z y g o g r a p t i d s h a p e , to a m u l t i r a m o u s shape. T h e siculae in all these s p e c i m e n s are identical in d i m e n s i o n and d e v e l o p m e n t . T h e r e f o r e it is not a t t e m p t e d to differentiate t h e m based on the distal r h a b d o s o m e d e v e l o p m e n t . T h e sicula is 1.1-1.2 m m l o n g and n e a r l y parallelsided. The p r o s i c u l a m e a s u r e s 0.5 m m in length and is 0.2 m m wide at the aperture, w h i c h bears a slight rutellure. T h e origin o f t h l 1 is 0.4 m m b e l o w the apex o f the sicula in the lower part o f the p r o s i c u l a . The theca bends s h a r p l y at 0 . 2 5 - 0 . 3 m m a b o v e the sicular aperture to p r o d u c e stipe one. T h e r e is no p r o x i m a l end dicalycal theca in any o f the r h a b d o s o m e s a n d t h l 1 p r o d u c e s th21 in a n o r m a l distal d e v e l o p m e n t fashion as is used to f o r m later thecae on this stipe. T h e stipes are 0.2 m m w i d e initially b e t w e e n apertures. T h e width at the apertures o f the first thecal pair is a b o u t 0.3 m m . D i s t a l l y the stipes w i d e n to values o f 0 . 4 - 0 . 4 5 r a m . The thecal overl a p is 0 . 3 5 - 0 . 4 m m . 2 T R D w a s m e a s u r e d with 1.9 mm at th2 in 2 s p e c i m e n s . Distal f r a g m e n t s show a 2 T R D o f up to 2.1 m m . A slight u n d u l a t i o n is c r e a t e d b y the origin o f each theca d o r s a l l y on its p a r e n t theca. Distal b r a n c h i n g occurs in s o m e s p e c i m e n s , usually after the formation o f two thecae. Thus, th41 appears to be the first distal d i c a l y c a l theca. The m u l t i r a m o u s r h a b d o s o m e s are based on an a z y g o g r a p t i d p r o x i m a l shape without an initial - p r o x i m a l - d i c h o t o m y . Two s u c c e s s i v e branchings are noted in one s p e c i m e n . R e m a r k s : This species shows a quite u n e x p e c t e d combination o f the lack o f p r o x i m a l d i c h o t o m i e s with normal d i c h o t o m o u s b r a n c h i n g p r e s e n t distally. As a n u m b e r o f s p e c i m e n s are f o u n d with the a z y g o g r a p t i d c o n d i t i o n , it is a s s u m e d that this is the n o r m a l developm e n t in the species and not a m a l f o r m a t i o n o f an individual s p e c i m e n . The presence o f t h e s e features indicates that the d e v e l o p m e n t o f p r o x i m a l a n d distal d i c h o t o m i e s m i g h t be i n d e p e n d e n t o f each other. E v e n the lack of a p r o x i m a l d i c h o t o m y does not force the c o l o n y to develop a different w a y o f b r a n c h i n g (e.g. cladial branching), but m i g h t keep the potential o f d i c h o g r a p t i d branching.

S i g m a g r a p t i n e sp. 4 (Figs. 6G, K , M , V, X) D e s c r i p t i o n : T h e species p o s s e s s e s a m u l t i r a m o u s rhabd o s o m e with v a r i o u s l y p l a c e d d i c h o t o m i e s . T h e sicula is 1 . 1 - 1 . 4 m m in length, p a r a l l e l - s i d e d through m o s t o f its length. The p r o s i c u l a is 0 . 3 - 0 . 3 5 m m long and slightly w i d e n i n g . Its apertural w i d t h is 0 . 2 - 0 . 2 2 m m , whereas it is 0 . 3 - 0 . 3 5 m m long. The sicular aperture bears a short rutellum o f less than 0.1 m m . T h e p r o x i m a l d e v e l o p m e n t is i s o g r a p t i d , dextral with a strong a s y m m e t r y . S p e c i m e n s in w h i c h stipe one is long and u n b r a n c h e d (up to 4 thecae) a n d b r a n c h e d forms with the first distal d i c h o t o m y at th31 can be found. T h e thecal apertures are 0 . 4 - 0 . 4 5 m m w i d e . 2 T R D r e a c h e s values b e t w e e n 2 . 3 2.4 m m in the p r o x i m a l end. Distal values are not available.

R e m a r k s : The species differs f r o m S i g m a g r a p t i n e sp. 3 in a slightly m o r e r o b u s t r h a b d o s o m e and an i n v a r i a b l y isograptid p r o x i m a l d e v e l o p m e n t o f the two-stiped to m u l t i r a m o u s c o l o n y . T h e p r o s i c u l a is p r o p o r t i o n a l l y s m a l l e r than in S i g m a g r a p t i n e sp. 3.

Acknowledgements The here documented fauna was investigated as part of the Ph.D. thesis of the author, supported by grants from the German Science Foundation (DFG grants Er 96/6-1; Er 96/6-2). The material was provided by B.-D. ERDTMANN (TU Berlin, Germany). Bernd KLEEBERG and Hanne GLOWA (TU Berlin, Germany) are acknowledged for their help with the photography.

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