Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 70. (Budapest 1978)

Vörös, A.: Viallithrys gen. n. (Terebratulida, Brachiopoda) from the Mediterranean Lower Jurassic

Genus Viallithyris gen. n. D e r i V a t o n o m i n i s : after the name of Mrs. Prof. GIULIA SACCHI VIALLI who was the first to study the internal features of the type species. Type-species: V. gozzanensis (PARONA), by monotypy. Diagnosis: Medium sized terebratulids, subpentagonal in outline, valves equally biconvex. Anterior commissure sulcate, shell surface capillate. Umbo slightly incurved, beak ridges blunt, foramen mesothyridid to permesothyridid. Outer hinge plates horizontal, crural bases given off dorsally, loop short. Brachidium support present. Discussion: Viallithyris has a rather unique internal morphology. Among the Mesozoic genera reviewed in the "Treatise" (MUIR-WOOD 1965) only Gibbithyris, Ornatothyris and Concinnithyris have subhorizontal hinge plates and crural bases given off dorsally but they are known only from the Upper Cretaceous and hence certainly not directly related to Viallithyris. — Recently, some new genera have been erected by TCHORSZHEVSKY (1974) from the Middle and Upper Jurassic beds of the USSR, namely, Psebajithyris, Muirwoodella and Karadagithyris which show internal features similar to Viallithyris, especially in the cardinal parts. Karadagithyris even has something like crural plates which were qualified by TCHORSZHEVSKY as outgrowths of the outer hinge plates. However, Karadagithyris and Muirwoodella belong to the long-looped terebratulids and can be excluded from subsequent discussion. Psebajithyris is short-looped and appears to be closely allied to Viallithyris. Correct comparison between the two genera is not possible since both are monotypic as yet but some important differences can be recorded. Psebajithyris has a uniplicate or biplicate anterior commissure and a very indistinct pedicle collar in contrast to the sulcate commissure and the strong and large pedicle collar of Viallithyris; their stratigraphie ranges are also different: Upper and Lower Jurassic, respectively. Distribution: Lower Jurassic of the Southern and Northern Limestone Alps and Bakony Mts. (Hungary). Fig. 1. Variation of width (W) against length (L) of 73 specimens of Viallithyris gozzanensis (PARONA)