Cometograptus nevadensis ( Berry and Murphy, 1975 )

Kozłowska-Dawidziuk, Anna, 2002, Agastograptus, a synonym of Plectograptus (Retiolitidae, Graptolithina), Acta Palaeontologica Polonica 47 (3), pp. 459-467 : 465

Cometograptus nevadensis ( Berry and Murphy, 1975)

Fig. 3D .

Retiolites nevadensis n. sp.; Berry and Murphy 1975: 100, pl.15: 5, 6.

Agastograptus nevadensis (Berry and Murphy) ; Obut and Zaslavskaya 1983: 107.

Spinograptus nevadensis (Berry and Murphy) ; Lenz 1993: 23, pl. 19: 1–6, pl. 20: 1–7.

Cometograptus nevadensis (Berry and Murphy) ; Lenz and Kozłowska−Dawidziuk 2001: 18, pl. 11: 1–6.

Diagnosis.—See Kozłowska−Dawidziuk 2001.

Discussion.— Cometograptus nevadensis is recognized as a species of the Cometograptus group restricted to the Cyrtograptus lundgreni Biozone (Kozłowska−Dawidziuk 2001) . The crucial difference between Plectograptus and Cometograptus is in the position of seams on the ancora sleeve lists, which may indicate the mode of list secretion, whether from the outside or from the inside (Bates and Kirk personal communication 1999). In Cometograptus seams on lists face out, the opposite of Plectograptus . There are also differences in arrangement of the ventral wall lists, presence of transverse rods, and development of apertural processes as a spine−like genicular hoods with seams, probably signifying some kind of membrane between them.

Occurrence.— Cometograptus nevadensis occurs in two places: Arctic Canada and Central Nevada, North America, both in Cyrtograptus lundgreni Biozone.

Figures

Fig. 3. A, H. Spinograptus munchi (Eisenack, 1951), A. ZPAL G. 27/3, EEP, Bartoszyce borehole, depth 1626.6 m, reverse view of mature rhabdosome. H. ZPAL G. 27/7, EEP Mielnik borehole, depth 1044.0 m, enlargement of paired apertural processes of distal theca. B, E, F. Neogothograptus balticus (Eisenack, 1951), Baltic erratic boulder 46 from Jarosławiec. B, E. ZPAL G. 27/4 mature rhabdosome with appendix (photo D. Bates). B. Reverse view. E. Ventral view of thecae 12 side. F. ZPAL G. 27/5 enlargement of single reticular apertural process. C, G. Spinograptus clathrospinosus (Eisenack, 1951), C. GSC120736, Arctic Canada, Cornwallis Island, AB−97 25 m, stereopair of immature rhabdosome, reverse view (modified after Lenz and Kozłowska− Dawidziuk 2002: fig. 13: 6). G. ZPAL G. 27/6, EEP, Bartoszyce borehole, depth 1631.2 m, paired apertural processes of medial theca. D. Cometograptus nevadensis (Berry and Murphy, 1975), GSC 99161, Arctic Canada, Cornwallis Island, SBC10E (modified after Lenz 1993: pl. 19: 1), ventro−latral view of rhabdosome. Scale bars 1 mm except for D, F–H which is 0.5 mm. Abbreviations as Fig. 2.