OP SOUTHERN INDIA. 283 



Astarte ? The eases are perfectly similar (see p. 273, etc.). A sliijht alteration of 

 an organ for a certain purpose may not always be equivalent to a cliange in the 

 entire organisation of the animal ! 



33. Cardita, Brug., 1789, fActbwholus* Klein, apud II. and A. Adams). 

 Shell rounded or cordiform, strongly radiately rihhed ; hinge with one strong 

 triangular cardinal tooth in the right and two teeth in the left valve, the posterior 

 one being moderately elongated ; anterior muscular impression somewhat elongated 

 with a small pit above it, posterior muscular impression broadly oval, pointed above. 

 Type, Car. sulcata, Lam. I have already pointed out the difficulty in properly 

 distinguishing between Venericanlia and Cardita. We must await further examina- 

 tion on this point. In the determination of the shell we shall very probably not 

 be able to make use of these indicated generic distinctions. Cardita is sparingly 

 represented already in the early mesozoic epoch and continues up to the present 

 time. 



Conrad called some of the cretaceous species at first Pseudocardia (Am. 

 Journ. Couch., 1866, ii, p. 103), for which name he subsequently sulistituted 

 Vetocardia (ibid, 1868, iv, p. 2IG), as the type of which Venericardia Dupiniana, 

 d'Orb., can fairly be taken. I have perfect specimens of both the valves of this 

 species before me, and I can see no great difference between them and other 

 typical Cardites, — form of shell, hinge-teeth, muscular and pallial impressions are 

 almost perfectly identical in both, except perhaps that the posterior cardinal teeth 

 are less elongated and thicker. In one large specimen of the left valve, there is, 

 as already stated, a distinct indication of a posterior lateral tooth, but in two 

 other somewhat smaller well preserved valves there is no trace of it. If at all 

 distinguished from Cardita these forms are identical with Falceocardita, (see p. 280), 

 but certainly the name Vetocardia has no signification. In vol. v, p. 48, of Am. 

 Journ. Conch., Conrad gives a fresh characteristic of the hinge from a Haddon- 

 field specimen. It quite agrees with that of Ven. Dupiniana of d'Orbigny. 



3-1. 3Iytilicardia, Blainv., 1821. Shell elongated and tumid, hinge-teeth 

 quite similar to those of Cardita, but thinner, internally insinuated below the 

 beaks, and generally somewhat more elongated than in the former genus; anterior 

 muscular impression rounded, posterior somewhat elongated. Type, 31. calyculata, 

 Brug. 



The difference between 3Ii/tilicardia and Cardita is to a certain extent really 

 a structural one, though at first it does not appear to be very marked. The very 

 inequilateral form of the shell with almost quite anterior or sub-terminal tumid, 

 but very closely approached beaks, causes an essential and constant change in 

 the form of the hinge-teeth, though their nmnber remains quite the same. 

 H. and A. Adams say that the posterior cardinal tooth in the left valve is 

 double, which is comparatively rarely the case, and I have not seen a single 



* Pending the difFerenccs to be yet traced out between the former and the present genns, I think it more advisable 

 not to introduce Klein's name, but retain that of Bruguiere, especially as it had been shortly after its proposition 

 carefully emended by Lamarck. 



3 z 



