146 Prof. E. Forbes on Fossil Invertebrata from ^Southern India. 



The differences presented by this shell at different periods of its growth and in 

 various states of preservation are very remarkable, and, unless noted, sure to mis- 

 lead. When young (fig. 15) it is a nearly smooth shell, of a more or less suborbi- 

 cular or quadrate form, strongly and angularly truncate at the siphonal side, and 

 there marked by longitudinal striae. When full-grown it becomes ovate, the angu- 

 lation gradually disappears, the siphonal side is marked by obscure striae which 

 suddenly cease at the angle, the opposite side is quite smooth, and the interspace 

 is marked by close, regular, numerous concentric sulcations. But whether old or 

 young, if it be decorticated, the markings of the surface become altogether dif- 

 ferent ; the siphonal truncated portion becomes deeply punctato-striate, and the 

 whole of the remainder of the shell is finely decussated. 



This Cardium belongs to the same group with Cardium subhillanum, C. sphee- 

 roideum, C. concentricum, and other cretaceous forms. It is very near to the last- 

 named species, from the greensand of Halden. 



Locality, Trinchinopoly. 



6. Cardium Hillanum, Sowerby. 



I have not thought it necessary to figure this species, as the specimens agree in 

 every essential character with British examples from Blackdown. The transverse 

 sulcations are rather coarser than in ordinary varieties, but after comparing the 

 Indian species with a considerable suite of the European, I could not draw any line 

 between them, since varieties exactly corresponding occurred among the latter. 



Locality, Verdachellura and Trinchinopoly. 



Genus Isocardia, Lamarck. 



1. Isocardia subsinuata, sp. nov. PI. XVII. fig. 12. 



I. testa suborbiculari, inflata, concen trice regulariter sulcata, latere antico obsolete tri-sinuato, 

 umbonibus prominentibus, distantibus, incurvatis. 



Length Of inch. Breadth 0-f^ inch. Thickness 0|§ inch. 



This very beautiful and well-marked Isocardia needs no further description than 

 that given in the diagnosis. It is very distinct from any species with which I am 

 acquainted. 



Locality, Pondicherry. 



Genus Venus, Linnaeus. 

 1. Venus arcotensis, sp. nov. PL XV. fig. 19. 



V. testa orbicular!, subobliqua, inaequilaterali, plus minusve convexa, polita, concentrice striata, 

 striis confertis, irregularibus, margine laevi, umbonibus prominentibus, lunula minuta. 

 Length If"^ inch. Breadth If^ inch. Height of a valve 0-^^ inch. 



