Pernostrea Munier-Chalmas, 1864

Kosenko, Igor N., 2017, Late Jurassic-Early Cretaceous oysters from Siberia: A systematic review, Acta Palaeontologica Polonica 62 (4), pp. 759-778 : 765

Genus Pernostrea Munier-Chalmas, 1864

Type species: Perna bachelieri Orbigny, 1850 (= Ostrea luciensis Orbigny, 1850 ), Bathonian of France.

Emended diagnosis (modified from Stenzel 1971: N1104). — Shells medium to large, equivalve or inequivalve. Outlines rectangular, deltoid or crescentic. Some species have well developed marginal growth foliations. Ligament area ostreoid, occasionally multivincular, large, very broad, rectangular to trapezoidal. Attachment area small to very large (almost all of LV). Angle between resilifer and commissural plane usually around 10–30°. PAM medium to large, circular to oval, clearly marked with a central to posterocentral position. No umbonal cavity. No chomata. Surface of valves covered with commarginal growth squamae. RV of some species covered by radial striae. Some species bear concentric plications and radial plicae (SOM: fig. 1A 2). The crescentic depression for the gills and the brachytellum is well developed. Microstructure consists mainly of regularly foliated structure, but some species have interlayers with?herringbone cross-foliated structure.

Remarks.— The name of the genus is based on the presence of a multivincular ligament, but actually only a few specimens of Pernostrea show this feature. This feature might be restricted to the type species.

Stratigraphic and geographic range.— Middle–Upper Jurassic of Europe (Alps, Poland, Romania, France, Germany, England, Switzerland) and Greenland, Lower Cretaceous of the Urals and the north of Eastern Siberia.