394 CRETACEOUS PELECYPODA 



distinguished from other similar forms by the presence of radiating ribs. The 

 fibrous layer appears to be often tliinner in Actinoceramus than in most of the 

 concentrically sulcated Iitocerami. 



19i. Volciceromus I would suggest for the type I. inwlntus, Sow., which 

 has the left valve strongly involute almost like a Nautilns, or somewhat resembling 

 a Gri/ph(Ba, while the right valve is very much smaller, flattened, slightly tumid 

 at the apex, resembling an operculum ; ' the hinge line is curved, conformed to the 

 ovately rounded aperture of the left valve, thickened and provided with numerous 

 ligamental pits, as in other typical species of the genus. 



20. Anopcea, Eichw., 18G1, (Leth. Ross., xme livr., 18G7, p. 479). Equivalve, 

 inequilateral, elongated, with the shorter anterior part narrower, beaks close toge- 

 ther, with a deep circumscribed lunule in front of them ; ligament situated in a 

 number of roundish pits in the straight cardinal margin, which has a rib-like tooth 

 in the left valve below the beak, extending anteriorly for a short distance. Type, 

 A. lohata, Auerb. and Frears. Eichwald refers two other species to this genus; 

 all three are from cretaceous deposits ; it principally differs from Inocermmis by the 

 presence of a deep lunule and by the internal hinge rib (in the left valve). 



21. Tidmnites, Defr., 1824-, (Diet. des. sc. nat., vol. xxxii, p. 316, and vol. xliv, 

 p. 107, cum fig.). Shell rather thin, rounded or oval, moderately inflated, liga- 

 ment almost internal, situated in seven or eight elongated, sub-parallel or slightly 

 diverging pits ; type, P. Adansonii, Defr. The geological position of this species 

 is unknown; it is said to have been found at Pavrille, and is either from Jurassic 

 or cretaceous beds. D'Orbigny (Pal. fran9. cret., vol. iii, p. 522,) does not describe 

 Defrance's species, as he had no specimen of it. But it is figured in the Diet, d, 

 sc. nat., and reproduced by Chenu in his Manual. This shell singularly recalls the 

 original figure of Conrad's Lyrodesma. 



D'Orbigny (1. cit.) notices a new species from the Oxfordien of Eochelle 

 under the name of P. ohlonga. In the Prodrome (vol. ii, p. 24,) the same author 

 states that the genus is now perfectly known, and that it is an Anomya with the 

 hinge of a Perna. He does not mention the former Oxfordien species, but calls 

 one from the Corallien of Eochelle, found attached to corals, P. Bujiellensis. To 

 all appearance the two names have been applied to the same shell. In the Joium. 

 de Conch, for 1853, p. 435, d'Orbigny considers Defrance's Pulcinites to be a 

 ' Perna' = Melina, and proposes for P. Piqiellensis a new generic name, Mi/potrema, 

 which, according to him, combines the characters of Melma and Anomija, having in 

 the lower or larger valve a round opening close to the umbones. If this character 

 of the valve is correctly stated and does not depend upon an accidental removal 

 of an attached portion of the shell, there would be little doubt as to the propriety 

 of the genus Uypotrema. But what relation this species, and another called 

 S. t>Hai}ff/ilaris, hears to the imperfectly known Pnli-lnltes remains yet to be proved. 

 Deshayos (Paris foss., 2ud edit., ii, p. 38,) is disposed to consider both as the same. 

 I never had an opportunity of examining any of these shells, and am, therefore, 

 unabla to form an opinion as to the value and relation of the tAvo proposed genera. 



