or SOUTHERN INDIA. 247 



the liinge-tecth from this geuns. This typical species has internally a short 

 posterior rib extending from the beak to about half the height of the shell, termi- 

 nating near the posterior muscular impression, and the impression of this rib on 

 the cast appears to have led to its having probably been taken as indicating a deep 

 pallial sinus, and consequently it was thought to belong to Thetironia = Thetis 

 of Sowerby. The species also greatly recalls the genus Serr'q)es (of the 

 Cardiidm), but it seems to diflPer from it sufficiently by the form and position of the 

 cardinal teeth and the total want of lateral teeth, though a further close com- 

 parison of perfect specimens of both genera would be very desirable. 



4. Gonodon, Schafhceutl, 1863, (Sud-Bayerns Leth. Geog., p. 382). Iso- 

 cardia ovata, Goldf., (from Jurassic rocks) is taken as the type of this genus. The 

 shell is ovate, tumid, apparently smooth ; the hinge of the right valve is described 

 as consisting of a very large median semi-circular broad tooth with the sharpened 

 edge turned upwards, that of the left valve with an equally large corresponding 

 pit below bounded by a long thick tooth somewhat smaller than that of the other 

 valve; the posterior margins of the hinge are thickened in both valves. This 

 genus is evidently allied to Uiiicardium, but seems to differ by the enormous 

 development (natural ?) of the teeth. 



5. SphreiHi, Sow., 1822, (Min. Conch., iv, p. 41, pi. 335 ; Pala;ocorbis,Coiivd.A, 

 1869, Am. Journ. Conch., v, p. 101). Shell ovate, inflated, solid, sub-equilateral, 

 liino-e of left valve with two blunt cardinal teeth, the posterior much smaller and 

 separated from the larger anterior by a pit, lunular edge somewhat extended with 

 a. deep pit and a swollen tooth-like margin above and below it, posteriorly with a 

 fm-row near the fulcral margin and several cross teeth at the posterior end, ligament 

 in a long excavated furrow. Type, Sphcera corruf/ata, Sow. = Corbis cordi/ormis, 

 d'Orb., from the Neocomien. Mr. Conrad forgot to notice the identity of the 

 species and hence a new generic name ! 



6. Mtitiella, StoL, 1870. Shell oblong, sub-equilateral, tumid, with obtuse 

 incurv^ed beaks, hinge in the left valve with two cardinal teeth, the anterior one 

 being sometimes bifid, in the right valve there is a single large bifid cardinal 

 tooth ; lunular edge expanded, with several teeth, or with more or less distinct 

 corrugations, representing anterior lateral teeth, posterior hinge side straight with a 

 furrow near the margin for the ligament, and an indistinct terminal posterior lateral 

 tooth. Type, Corbis rotundata, d'Orb. 



This genus differs essentially by the characters of the hinge from the previous ; 

 there are several middle and upper cretaceous species which belong to it, but none 

 are knowTi from more recent deposits. 



7. Spha;riola, StoL, 1870. Shell rounded, globose, nearly equilateral, with 

 concentric stria) or sulci on the surface, hinge with two diverging cardinal teeth in 

 each valve, the anterior being somewhat elongated and nearly horizontally extended. 

 Type, Sphcera Mudridi, d'Arch., (vide Morris and Lycett, Foss. Great Ool., 

 part ii, p. 71) ; the aljsence of lateral teeth and the usual rounded and globose form 

 readily distinguish this genus from the next, Some species belonging to it are 



3 p 



