Corbicularia Lyaschenko, 1973

Racheboeuf, Patrick, Phuong, Ta Hoa, Hung, Nguyen Huu, Feist, Monique & Janvier, Philippe, 2006, Brachiopods, crustaceans, vertebrates, and charophytes from the Devonian Ly Hoa, Nam Can and Dong Tho formations of Central Vietnam, Geodiversitas 28 (1), pp. 5-36 : 25-26

Genus Corbicularia Lyaschenko, 1973

TYPE SPECIES. — Chonetes menneri Lyaschenko, 1958 . Frasnian, Russian Platform.

DISCUSSION

In the literature, four chonetoidean genera, namely Striatochonetes Mikrjukov, 1968 , Rhyssochonetes Johnson, 1970 , Corbicularia Lyaschenko, 1973 , and Cedulia Racheboeuf, 1979 , have been defined as including in their diagnosis concentric fila crossing the radial ornament. Cedulia has already been considered as a junior synonym of Rhyssochonetes ( Racheboeuf 1981, 2000). The relationships between Striatochonetes , Rhyssochonetes , and Corbicularia have also been discussed ( Johnson 1978; Racheboeuf 1981), but the question remained unanswered, mainly because the preservation of the original specimens is different. The former of these three genera, Striatochonetes , was defined with Strophomena setigera Hall, 1843 as the type species. However Strophomena setigera exhibits no more than three to four concentric growth lines and lacks the typical concentric fila which are included in the original diagnosis, as established by Johnson (1978), and which are well developed in S. krylovae Mikrjukov, 1968 ( Mikrjukov 1968: pl. 33, figs 3, 4). The genus name Striatochonetes has thus to be restricted to the type species S. setigera Hall, 1843 , until the species is carefully revised.

The shell of Corbicularia Lyaschenko, 1973 is morphologically very close to that of Rhyssochonetes Johnson, 1970 , and Johnson (1978: 125) considered that Corbicularia was a probable junior synonym of Rhyssochonetes . The main difference lies in: 1) a less transverse, more rounded, shell outline in Corbicularia than in Rhyssochonetes ; 2) the orientation of the spines, which are at 45° in Rhyssochonetes , and high-angled to perpendicular in Corbicularia ; and 3) the development of a pair of long but faint accessory septa in Corbicularia , at least in the species C. cracoviensis Balinski, 1979 . Although the species assigned to Corbicularia , all from the Givetian and Frasnian of the Russian Platform, are poorly known internally, the two genera, Rhyssochonetes and Corbicularia , are here still provisionally regarded as distinct. The species Striatochonetes ? parisi Racheboeuf, 1981 , and S.? goasquellouensis Racheboeuf, 1981 are reassigned to Corbicularia according to their shell size and outline, and high-angled spines.