Rafinesquina, Hall & Clarke, 1892

Modzalevskaya, Tatiana L., 2003, Silurian and Devonian brachiopods from Severnaya Zemlya (Russian Arctic), Geodiversitas 25 (1), pp. 73-107 : 76-77

Rafinesquina ? stropheodontoides ( Savage, 1913) ( Fig. 3 )

Brachyprion stropheodontoides Savage, 1913: 119 , pl. 6, fig. 4.

Rafinesquina ? inaequicostata Lopushinskaya, 1967: 87, pl. XX, fig. 2.

Rafinesquina ? stropheodontoides – Amsden 1974: 52, pl. 12, figs 2-4, pl. 13, fig. 1.

MATERIAL EXAMINED. — 13 specimens (separate ventral and dorsal valves and their fragments), from loc. 13A, bed 124, Matusevich River , October Revolution Island ( Männik et al. 2002: figs 2, 5) ; Vodopad Formation.

REMARKS

The specimens are characterized by a concavoconvex, subquadrate general outline of shell, lack of a well defined geniculation, and a low interarea. The hinge line is straight, and the cardinal extremities are alate. The surface is finely costellated, with four to five minor costellae, presented in the interspaces between the major ribs. A single, straight, strong median costa extends along the whole shell length. Other costae curve near

A

B

the cardinal extremities. The costellae are crossed by short and undulate rugae.

The shape and ornamentation of R.? stropheodontoides are similar to those of R. crispa Andreeva, 1961 studied from the Dolborian Stage of East Siberia ( Nikiforova & Andreeva 1961: 159, pl. XXIX, figs 5, 6). The distinguishing features of the former include a median thickened rib and irregular thickening ribs. These are the earliest representatives of the genus found in the Arctic region. They have previously been known only from the Edgewood Formation (Ashgill-lowermost Llandovery) of North America.

Figures

FIG. 3. — Rafinesquina? stropheodontoides (Savage, 1913); A, C, partly damaged dorsal valve, showing thickened costellae at different distances from the beak and short undulate rugae (N 6/12991); A, dorsal view; C, enlarged surface sculpturing; B, ventral view of a pedicle valve (N 7/12991), loc. 13A, bed 124, Vodopad Formation. Scale bars: A, B, 6 mm; C, 2 mm.