Paromoeopygma Sartenaer, 1968

Sokiran, Elena V., 2002, Frasnian-Famennian extinction and recovery of rhynchonellid brachiopods from the East European Platform, Acta Palaeontologica Polonica 47 (2), pp. 339-354 : 349-352

Genus Paromoeopygma Sartenaer, 1968 Paromoeopygma koscharica ( Nalivkin, 1934)

Figs. 14F–M , 16.

Pugnax koscharica n. sp.; Nalivkin 1934: 24, pl. 2: 1–3.

Pugnax koscharica Nalivkin ; Ljashenko 1959: 205, pl. 75: 7. Paromoeopygma koscharica Nalivkin ; Pushkin 1986: 73–74, pl. 1: 6.

Emended diagnosis.— P. koscharica differs from type species of genus P.bellicastellana Sartenaer, 1968 , mainly by its parallel or slightly divergent dental plates and laterally directed crura, while P. bellicastellana is characterized by divergent dental plates and dorso−laterally directed crus.

Neotype.—Complete shell from the Nalivkin collection CNIGR 1085 /4572, Fig. 14F–I .

Material.—Five well preserved shells (including three specimens from Nalivkin’s collection).

Description.—Shellmedium−sized,dorsibiconvex,subelliptic to suboval in outline; short curved hinge line, lateral and anterior margins rounded; anterior commissure uniplicate.

Ventral valve moderately convex, beak small, slightly incurved,wideandshallowsulcusstartsatanteriorpartofthe valve, tongue high and rounded. Dorsal valve deeper than ventral valve; weakly defined fold begins at anterior part of the valve.

Shell smooth with exception of coarse, rounded ribs developed near the anterior margin only. Microornamentation of radial striae (8 per 1mm); growth lines rarely preserved. Internally with nearly parallel dental plates; median septum absent. Crural bases directed laterally.

Remarks.—Originally this species was referred by Nalivkin (1934) to Pugnax , but he noted, that fine radial striae on the surface of the shell of P. koscharica distinguish it from other species of Pugnax . Furthermore he noted, that presence of striae is a very important feature and possibly this species should be assigned to a new genus ( Nalivkin 1934; Pushkin 1986). On the base of microornamentation Pushkin (1986) transferred Pugnaxkoscharica to Paromoeopygma . Furthermore, he assigned to this genus some early Famennian species from Byelorussia: P. janischevskii , P. sergei . It should be noted, that P. komarovichensis , which he included in Paromoeopygma (see Pushkin 1986: 73), is the type species of his genus Striatorhynchus (see Pushkin 1986: 91); it follows that probably his attribution to Paromoeopygma was a mistake. All these species are characterized externally by presence of fine striae, internally by parallel dental plates and absence of dorsal septum, except Striatorhynchus komarovichensis that has a dorsal septum. Although these species have similar internal and external morphology to Paromoeopygma , they differ from P. koscharicus generally by their shorter dental plates.

Occurrence.—Early Famennian, Pa. crepida – Pa. rhomboidea zones, Elets Horizon, central Russia; Byelorussia.

Figures

Fig. 14. A–E. Globulirhynchia minima sp. nov. from late Frasnian, Evlanovo Horizon, Chlevnoe village, Don River Basin. A–D. Holotype, CNIGR 13/13076, ventral, dorsal, lateral, and anterior views, × 5. E. CNIGR 14/13076, × 2. F–M. Paromoeopygma koscharica (Nalivkin, 1934) from early Famennian, Zadonsk Horizon, Koschary village, Zadonsk region. F–I. Neotype, CNIGR 1085/4572 ventral, dorsal, anterior, and lateral views, × 1.5. J–M. CNIGR 1083/4572, × 1.5.