Coolinia gracilis (Andreeva, 1961)

Modzalevskaya, Tatiana L., 2003, Silurian and Devonian brachiopods from Severnaya Zemlya (Russian Arctic), Geodiversitas 25 (1), pp. 73-107 : 79

Coolinia gracilis (Andreeva in Nikiforova & Andreeva, 1961) ( Fig. 6 )

Schellwienella gracilis Andreeva in Nikiforova & Andreeva, 1961: 192, pl. XLI, figs 3-8.

Coolinia gracilis – Lopushinskaya 1991: 53, pl. I, fig. 6.

MATERIAL EXAMINED. — Four specimens embedded in rock matrix from loc. 13A, beds 124 and 140, Matusevich River ; two specimens from loc. 32, beds 6- 7, Ushakov River ; and two specimens from loc. 29a, Lednikovaya River , October Revolution Island ( Männik et al. 2002: figs 1, 2, 5, 6) ; Vodopad Formation.

REMARKS

The specimens are characteristically relatively large in size (L = 20.5-24.8 mm, W = 19.7-26.0 mm). Unequally biconvex or slightly convexoconcave shells are rounded in general outline, and possess a radial parvicostellate ornament with one or two new costellae arising exclusively by intercalation. Coarse concentric growth filae are presented across the costellae. The external morphology of the studied shells is typical of C. gracilis , but the dimensions of the chilidium and pseudodeltidium are not clear. O. N. Andreeva noted the low plane ventral unterarea with delthyrium bearing a small, flat pseudodel- t i d i u m i n i t s a p e x o n S i b e r i a n s p e c i m e n s ( Nikiforova & Andreeva 1961: 192). Coolinia gracilis a p p e a r s b e f o r e C. gorbiyatchensis Lopushinskaya, 1976 from Talikit and Omnutakh formations, and differs in larger size and equally spaced ribs ( Lopushinskaya 1976: 95, pl. XXI, figs 11-13). The species resembles Coolinia propinqua (Meek & Worthen, 1868) , redescribed by Amsden (1974: 57, pl. 2, fig. 3, pl. 3, figs 1-5, pl. 4, fig. 1) from the Edgewood Formation in the Alexandrian Series of North America. The latter may be a senior synonym of C. gracilis .

Figures

FIG. 6. — Coolinia gracilis (Andreeva in Nikiforova & Andreeva, 1961); A, ventral view of a pedicle valve (N 13/12991); B, C, dorsal view of a damaged brachial valve (N 14/12991), loc. 29a,?Vodopad Formation. Scale bars: A, B, 6 mm; C, 10 mm.