OF SOUTHERN INDIA. 



209 



3. Lcevicardhim, Swains., 18-iO. Shells obliquely cordate, more or less 

 inflated, usually solid, with the radiating ribs on the surface small and thin 

 sometimes hardly traceable, especially at the anterior and posterior end ; hiu"-e 

 line curved, teeth stout, distinct, but not very prominent ; muscular impressions 

 very large, the posterior especially so; pallial line truncate or very slightly in- 

 sinuated. Card, oblong iim, Chem., is one of the best known and typical forms 

 already quoted by Swainson. Species of Lcevlcardium (proper) are rare in the 

 mesozoic strata ; they mostly appear to be represented from the tertiary upwards, 

 while in former times they seem to be rejilaced by the next. 



4. Frotocardium, Beyrich, 1845, (Zeitsch. f, Malakozoologie, p. 17). Shell 

 obliquely cordate, varying in length exactly like Lcevicardium, outer surface con- 

 centrically striated or ribbed, except on the posterior half or so, where radiatino- 

 ribs occur ; hinge typical ; posterior muscular impression very large, and in some 

 species the shell below it peculiarly flattened or even slightly impressed ; tvpe 

 Card, hillanum, Sow., from cretaceous rocks. In this species Beyrich particularly 

 notices the posterior sinus of the pallial impression, it being here more distinct than 

 in most other closely allied forms, though even in this species its size is especially 

 due to the peculiar prolongation of the posterior muscular impression. The 

 presence of the sinus is, however, not an essential character of the sub-o-enus 

 for there are several species to be noticed in which the pallial line is hardly truncate. 



Pachycardmm is proposed by Conrad (Am. Journ. of Conch., vol. v, p. 96,) 

 apparently only to include two cretaceous species, Card. Spilmani, Con., and 

 C. bisectum, Forb. The latter is an Indian species, and I have had therefore full 

 opportunity of testing Mr. Conrad's characteristics. The difference from the type 

 species of Frotocardium is stated to consist in the greater height in proportion to 

 length of the shell; all the other characters mentioned by Conrad are a repetition 

 of those of P. hillanum, and partially also of the recent LcemGardium. The height 

 in proportion to length of C. bisectum is certainly not of a generic or sub-generic 

 importance, as clearly illustrated by the second species Frotoc. Fondicheriense, 

 which is intermediate between it and F. hillanum. We have in such species only 

 perfectly similar changes of form as, for instance, we observe in Lceo. serratum 

 and Norcegicum, and several others. 



The recent Cardium ^olicum, Born, f = pectinatum, Linn.,) and C. lyratum. 

 Sow., are the representatives of the io%^A Frotocardia ; and the eocene forms, as 

 Card, parile, C. fraudator, Deshayes, (Paris fossils, 2nd edit., Atlas, pi. 54), 

 which have the radiating strige markedly stronger on the posterior end than on 

 the rest of the surface, are intermediate between the mesozoic Frotocardia and 

 the recent Lcevicardia, bu.t as they possess striae on the entire surface, and as the 

 inner margins of the shell are crenulated accordingly, they are nearer Lcevicardiiim 

 than Frotocardium ; all of them belong, however, only to one and the same type 

 of shells. 



5. Serripes, Beck, 1844. Shell broadly cordate, moderately thin, surface 

 smooth or nearly so, inner marginal edge not or very slightly crenulated, cardinal 



3e 



