Deltoideum Rollier, 1917

Kosenko, Igor N., 2017, Late Jurassic-Early Cretaceous oysters from Siberia: A systematic review, Acta Palaeontologica Polonica 62 (4), pp. 759-778 : 764

Genus Deltoideum Rollier, 1917

Type species: Ostrea sowerbyana Bronn, 1836 (= Ostrea delta Smith, 1817 ), Kimmeridgian of England and France.

Diagnosis (modified from Stenzel 1971: N1102). — Shells medium to large, equivalve, rare slightly inequivalve. Outlines deltoid, crescentic or spatulate. Some species have well developed marginal growth foliations. Ligament area ostreoid, high, narrow, triangular to trapezoidal. Resilifer shallow, well marked, usually triangular. Anterior bourrelet usually longer than posterior one. Attachment area small to very large almost all of LV). Angle between resilifer and commissural plane usually around 10°. PAM medium to small, circular, clearly marked with a posterocentral to posteroventral position. No umbonal cavity. No chomata. Surface of valves covered with commarginal growth squamae. RV of some species covered by radial striae. The crescentic depression for the gills and the brachytellum is well developed. Microstructure consists of regularly foliated structure ( Fig. 5A ).

Stratigraphic and geographic range (modified from Stenzel 1971: N1103). — Middle Jurassic (Bathonian)–Upper Jurassic Tithonian) of Europe ( England, France, Germany, Poland, European part of Russia) and Saudi Arabia; Berriassian of Mangyshlak ( Kazakhstan); Upper Jurassic (Kimmeridgian)– Lower Cretaceous (Hauterivian) of Siberia.

Figures

Fig. 5. Microstructure of studied gryphaeid oysters. A. Deltoideum delta (Smith, 1817), TsSGM 2068/87; Kimmeridgian, Dorset, England. B. Pernostrea uralensis (Zakharov, 1972), TsSGM 2068/45; Upper Volgian, Maurynya River, eastern slopes of the Northern Urals. Microstructure (A1, B1), cross section (A2, B2). RF, regularly foliated structure; HCF,?herringbone cross-foliated structure.