OF SOUTHERN INDIA. 351 



adultis nonminqnam etiam ohsoletis ; area ligamentali latissima, angulatim multi- 

 sulcata ; uinhonibus distantibits, incurvis, sub-sulcatis. Cardo in utroque latere plicis 

 3-1; elongatis, supra et infra denticulatis, instructus, anticis j^riDio paulo curvatis, 

 delude fere horizontaliter extensis, ptosticls parallelis ; deniibus mcdianis paucis, 

 parvis, obliquis, irrefftilarlbus ; impresslone musculari postica in lamina erecta, 

 elongata, sita ; margine inter no indistlncter pUcose denticulato. 



Average height of shell : its length .,, ... ... ahout 0'73 



Thickness „ : „ ... ... ... „ 070 



Length of largest specimen ... ... ... ... 80 m. m. 



The elongated oblique form and great convexity of the valves with the very- 

 wide ligamental area are particularly characteristic of this species. The two valves 

 are only slightly unequal, but the difference in the ornamentation is generally 

 very apparent. On the left valve the radiating ribs are distant, generally separated 

 by interspaces wider than the thickness of the ribs and sometimes marked with 

 intervening thinner ribs ; on the right valve the ribs are all about equally strong, 

 but they are placed much closer together. On the posterior declivity there only 

 exists a fine radiating striation, and even this becomes partially obsolete in large 

 specimens. The hinge is peculiar and slightly different from that of typical 

 Macrodon, but, as already noticed, (p. 336), I am not certain whether Meek's name 

 Grammatodon is sub-generically applicable to these forms. The hinge-teeth in 

 Macrodon are anteriorly very short, posteriorly very elongated. In the present 

 species the teeth, or rather hinge-ribs, are sub-equal on the two sides, the anterior 

 are first oblique, then bent outward, and prolonged almost horizontally, or slightly 

 sloping downwards, the posterior hinge-ribs are parallel throughout, and very nearly 

 quite straight, as in CucullcBa ; in the middle there are a few short somewhat irre- 

 gular teeth ; all the teeth and hinge-ribs are finely denticulated above and below. 

 The posterior muscular impression is situated on a raised, elongated plate. 



Localities. — Karapaudy, Arrialoor, ComarapoUiam, Ootacoil, &c., in whitish 

 sandstone ; very common. 



Formation. — Arrialoor group. 



2. Macrodon (? Grammatodon) disparile, d'Orblgny, PI. XX, Figs. 6-7. 



1817. Area disparilis, d'Orb., Voy. Astrol.abe, Paleont., pi. v, figs. 37-38. 



Mac. testa elongate suh-qnadrangularl, valde Inflata, antice suh-rotundata, 

 postlce oblique truncata, ab umbonibns ad termluatlonem postero-inferiorem obtnse 

 angulata aitt sub-carinata ; umbonibns latls, prominentlbus, incurvis, medio obsolete 

 uni-sulcatis ; sujjerfcle radiathn costata et strlis decussantibus confertissimis, preci- 

 pue in specimlnibus juniorlbiis dlstinctis, tecta, costis in mlva sinistra paulo distantio- 

 ribus quam in valva dextra ; decllvitate postica lata, paulo concaviuscula et radiatim 

 coitfertim striata ; area ligamentall lata, angulatim crasse lamellose striata. Cardo 

 2)licls ilentiformibus 3-4 anticis, angulatim externe recurvatis et prolongatls, mediis 



4 B 



