OF SOUTHERN INDIA. 51 



2. CardlUa, Desliayes, 1835. Shell ovate, liig-lier than long, tvimid, with the 

 beaks prominent and incurved anteriorly ; hinge with a large cartilage-pit in each 

 valve ; two cardinal teeth in the left and one in the right valve, one posterior mar- 

 ginal lamella projects into the space internally on which the muscular impression 

 is situated, pallial line simple. 



In external appearance, especially in the peculiar radiating stria? on the pos- 

 terior half of the shell, this genus again recalls Tagonia, but it is not gaping 

 posteriorly, and the internal, lateral lamellar tooth seems to he very characteristic. 

 Deshayes's classification of the genus next to Seterocardia certainly appears more 

 correct than that of some other authors who place it near Glossiis, {Isocardia, 

 auctorum) on account of the external resemblance of both. 



3. Strothodon, Giebel, 1856, (Abhandlg. des Nat. Ver. f. Sachsen und Thii- 

 ringen, I, pt. 1, p. 102). Eight valve tumid, high like CardiUa, beaks incurved, with 

 a groove running from the beaks to the posterior margin, hinge with a flat cardinal 

 tooth and with a second tooth projecting from its base below and anteriorly. Only one 

 valve (St. LiscaviensisJ , is known of this shell from the triassic beds of Liskau (Ger- 

 many). It has the general appearance of a CardiUa, but the hinge differs, and as 

 the teeth are flat, I suspect that at least the upper one indicates by its form 

 that it had supported a cartilage. Giebel says that an external ligament is also pre- 

 sent, but it must have been rather thin, for the fulcra are not perceptibly thickened. 

 In general appearance the shell bears also a great resemblance to Crijptodon and 

 to some species of Lticina, represented by the type L. columbella. 



4. Heterocardia, Desh., 1854. Shell subtrigonal, or transversally oval ; car- 

 tilage-pit wide, short, cardinal teeth thin, prominent ; anterior lateral very close 

 to the cardinal, short ; posterior, elongated ; pallial sinus very deep. 



5. Darwa, Gray, 1849. Shell oblong, rather compressed and slightly gaping 

 at both ends, umbones sub-central ; hinge with a large cartilage-pit, lateral teeth 

 very close to the cardinal, anterior shorter than the posterior ; ligament external, 

 sepai'ated from the cartilage by a shelly plate. 



6. Ccecella, Gray, 1849. Similarly oval as the last, anterior cardinal tooth 

 of left valve thick, and grooved at the end, the posterior cardinal and the two 

 teeth of the right valve very slightly prominent ; lateral teeth elongated, almost 

 equal, close to the cardinal and diverging ; ligament marginal, internally not sepa- 

 rated from the cartilage. 



There are several species of this genvis in the eastern seas, some of them appear 

 to be estuary, or at least partially so. I am not certain whether Darina is really 

 generically different from the present genus ; either of them may be considered as 

 a sub-genus of the other. 



7. Eaeta, Gray, 1849. Shell thin, ventricose, high, slightly produced pos- 

 teriorly and gaping ; cardinal teeth strong, the anterior much shorter than the 

 posterior ; lateral teeth thin, but distinct, close to the cardinal, highly diverging 

 from the beaks ; ligament marginal, situated in a deep groove but free above. The 

 thin, concentrically plicated shell is very characteristic for these forms, which are 

 probably estuary. 



