190 CRETACEOUS PELECYPODA 



each valve; ricjht valve with the supra-posterior cardinal tooth, generally bifid 

 anteriorly with a hook-like downward bent prolongation, infero-anterior cardinal 

 smaller, lamelliform, or more or less tubercular, separated from the other tooth by 

 a more or less horizontally extending flexuous groove into which the infero-anterior 

 cardinal tooth of the left valve fits, the supero-posterior cardinal of tliis valve is 

 moderately prolonged, single or indistinctly bifid. 



There appear to be thi'ee somewhat diff'erent forms belonging to this genus. 



Morton (loc. cit.) says of Veniella, " hinge with three robust cardinal teeth in 

 each valve." In the type species, V. Conradi, which he figures, the anterior bent 

 portion of the supero-posterior cardinal tooth of the right valve appears to be 

 rather strongly thickened at the end, and the other cardinal tooth below it has a 

 distinct projection to meet that thickening. The consequence is, that the groove 

 separating the two teeth and the corresponding tooth of the left valve are more 

 or less distinctly divided into two pits or teeth. This is exactly what is to be 

 already observed in the Jurassic Isocardla cordata, Buckmann (see Denksch. 

 Akad., Wien, vol. xxvii, pt. ii, p. 41, pi. 4, fig. 1), and the form of the shell as well 

 as of the hinge oi Isocardia ct/j^rinoides, Braun, (in Sandberger Conch, d. Mainzer- 

 Beckens, p. 315, pi. 25, fig. 2,) also appears to correspond well with Morton's 

 type. 



12a. In some other species, for which Munier-Chalmas (Jour, de Conch., 

 3"' ser., vol. iii, 1863, p. 288,) proposed the name Anisocardia* the hooked end of 

 the supero-posterior tooth of the right valve is very Little, and the antero-inferior 

 cardinal of the same valve scarcely thickened on the inner or upper side, except 

 very slightly at its base ; consequently the groove separating the two teeth is more 

 continuous, and the corresponding tooth of the left valve is flexuous, being con- 

 stricted only in the middle. The type species which M. Chalmas describes is 

 Anisocardia elegans from the Kimmeridge clay at Havre. 



Several cretaceovis species which I shall mention subsequently also belong to 

 this group which, as it mostly includes small forms with rather thin shells, may 

 be retained under the sub-generic name Anisocardia. Deshayes' Cypric. 

 acutangida and isocardioides, (Paris foss., 2nd edit., pi. 57), evidently also belong to 

 this sub-genus. 



12b. Venilicardia, StoL, 1870. This is suggested to include a third group of 

 the Veniella type, such as the cretaceous Cyprina bifida, and possibly also C. crassi- 

 dentata of Zittel, and our Ven. Arcotica, n. sp., or the tertiary Ci/prina tumida 

 of Nyst (Belg. foss.), and very likely also the Jurassic Cijpricardia cordiformis of 

 Deshayes, and several others. All these species are characterized by a strong, thick 

 shell, of large size, the supero-posterior cardinal teeth are as usually more or less 

 bifid, the one in the right valve with a very easy curve at the anterior end, the 

 antero-inferior cardinal teeth of both valves are long, flexuous, and their posterior 

 ends are in both cases strongly thickened and tubercular. Tliis distinction from 



* DoUfuss (Faune Kimm., 1863, pp. 23 and 71, pi. 10, figs. 9-14,) quotes the saiiip as A/^ora rilia . a namo wliich 

 M uuier first suggested, but afterwards altered without having given publicity to it. 



