CARDIID^. 193 



CARDIUM, restricted. (Tropidocardium, Romer.) Shell ven- 

 tricose, subeqilateral, more or less gaping behind ; niai'gin 

 strongly dentate ; valves covered with strong radiating ribs. 

 G. costatum, Linn, (cxvi, 70). 



BUCARDiUM, Gray. (Pectunculus, Adanson.) Shell globose, 

 solid, strongly ribbed, the ribs produced on the gaping posterior 

 margin into strong spine-like teeth. G. ringens, Chemn. (cxvi, 

 71). 



TRACHYCARDiUM, Morch. (Granocardium, Gabb. Criocar- 

 dium, Conrad, 1870.) Shell oblong, inflated, a little oblique, 

 radiatel}^ ribbed ; the tops or sides of the ribs scaly spinose. G. 

 muricatum, L. (cxvi, 72-74). West Indies. Fossil. Cret. ; 

 California. Criocardium is " Multiradiate, interstices spinose, 

 ribs smooth; anterior lateral tooth long and prominent." G. 

 dumosum , Gonr. Cret.; N.Jersey. The spines originate later- 

 ally on the ribs (as is not unusual in the genus), and not 

 between them. 



ACANTHOCARDTA, Gray, 1847. (Isocardia, Klein.) Shell sub- 

 globose, radiately ribbed, the ribs bearing strong, sharp, curved 

 spines. C. aculeatum, Linn, (cxvi, 75). 



CERASTODERMA, Poli, 1791. Shell subcordiform, rounded 

 behind ; valves close, flatly ribbed ; cardinal teeth strong. G. 

 edule, Linn. (Cxvi, 76). 



PAPYRiDEA, Swains., 1840. Shell oval, oblong or transverse, 

 thin, inequilateral; radiately ribbed, the ribs forming strong 

 marginal teeth posteriorly. C. hiulca, Reeve (cxvi, 77). 



ruLViA, Gray, 1847. Shell transversely oblong, very inequi- 

 lateral, posteriorly produced, radiately ribbed. Differs very little 

 from the last group. G. bullata, Linn, (cxvi, 78). 



LYMNOCARDiUM, Stol., 1870. (Pscudocardia [part], Conrad, 

 1866. Vetocardia [part], Conrad, 1868.) Shell elongated, 

 inequi valve, with the anterior side shorter, moderately inflated 

 and rather thin, surface radiately ribbed ; cardinal teeth two, or 

 one in each valve, small, and sometimes quite obsolete, lateral 

 teeth remote, more or less lamelliform, pallial line either entire 

 or (rarely) sinuated, posterior gape usually distinct. Type, 

 Gardium Haveri, Homes. The species are~Tertiary ; Eastern 

 Europe, W. Asia. The type is one of the species which Conrad 

 quotes under his genus Pseudocardia, the name of which the 

 same author subsequently replaces by Vetocardia. When giving 

 the characteristics of the latter, he evidently refers solely to 

 d'Orbigny's cretaceous Yenericardise, but how it was possible to 

 associate with these forms the first named ones and others 

 described by Homes from the uppermost tertiary beds of the 

 Yienna (or rather Hungarian) Basin, it is really difficult to 

 understand, and this the more when, after the enumeration of 



