OF SOUTHEEN INDIA. 351 



adultis nonmmquam etiam obsoletis ; area ligamentali latissima, angulatim mtdti- 

 sulcata ; mnhonibus distantibus, incurvis, sub-sulcatis, Cardo in utroqiie latere plicis 

 3-4 elongatis^ supra et infra denticulatis, instructus, anticis primo paulo ctirvatis, 

 deinde fere liorizontaliter extensis^ posticis parallelis ; dentibus medianis paucis, 

 parvis, obliqtds, irregularibus ; impressione musculari postica in lamina erecta^ 

 elongata, sita ; margine interna indistincter plicose denticulato. 



Average height of shell : its length ... ... ... about 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 Cucullcea ; 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, Gomarapolliam, Ootacoil, &c., in whitish 

 sandstone ; very common. 



Formation, — Arrialoor group. 



^ 2. Macrodon (? Geammatodon) disparile, d'Orbigny, PI. XX, Fio^s. 6-7. 



1847. Area dis;parilis, d'Orb., Voj. Astrolabe, Paleont., pi v, figs. 37-38. 



Mac. testa elongate sub-quadrangulari, valde i?iflata, antice sub -rotun data, 

 postice oblique truncaia, ab umbonibus ad terminationem postero-inferiorem obtuse 

 angulata aut sub-carinata ; umbonibus latis, prominentibus, incurvis, medio obsolete 

 uni-sulcatis ; superficie radiatim costata et striis decussantibus confer tissimis, preci- 

 pue in speciminibus junioribus distinctis, tecta, costis in valva sinistra paulo distantio- 

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

 confertim striata ; area ligamentali lata, angulatim crasse lamellose striata, Cardo 

 plicis dentiformibus 3-4 anticis, angulatim externe recurvatis et prolongatis, mediis 



