290 CRETACEOUS PELECYPODA 



from one to the other can, however, be traced in India as well as in Europe. 

 The form of the shell and its thickness is subject to a great deal of variation, as 

 may be seen by a comparison of our figures, and still more those given by Zittel. 

 The strongly sulcated form is designated by Zitttel as var. sulc/fera. I can see 

 no difference in his figures between the hinge of this variety and that of the 

 typical form ; we possess three left valves of the former from Southern India, and 

 one left and two right ones of the latter. Comparing these together the hinge 

 area of var. snlcifera is higher, the teeth longer, and the lunula deeper than in 

 the three specimens of the typical form ; but as the shells do not differ in any 

 other respect, I am inclined to regard with Zittel the variation to be within 

 the limit of specific character. 



LoGcdity. — Near Arrialoor, in grey soft sandstone ; not common. 



Formation. — Arrialoor group. 



2. Crassatella Zitteliana, StoUczJca, PI. V, Figs. 15-19. 



Cr. testa cuneiforme elongata, inceqiiilaterali, tumida, ad margmem lunularem 

 emarginata, antice breviter rotnndata, postice attenuata, sub-caudata et oblique 

 truncata, carina acuta ab umbonibus ad terminationem postero-inferiorem decurrente 

 instructa, concentrice costulata, costulis in regione umbonali crassis, periplieriam versus 

 tennioribits, confertis, postice fere omnino obsoletis ; Itmula elongato ovali, profunda, 

 Icevigata, margine acuto ciixitmscripta ; area longiore, angusta etiamque profunda. 

 Cardine dentibus cardinalibus anterioribus m utraque valva et fossa cartilaginigera 

 postica mediocriter excavata instructo, dente antico in valva dextra laterali ajtproxi- 

 mato, postico fere omnino obsoleto ; in valva sinistra dente laterali antico p>arvulo, 

 postico elongato, distinctiore. 



Height of shell : its length ... ... ... ... O'TJ. 



Thickness „ : „ ... ... ... ... 0-6-1 



The ornamentation of this species is, as likewise its peculiar pholadoid form, 

 very characteristic, strongly recalling the palaeozoic shells which have Ijeen called 

 Sedgwiclda. Near the umbones the concentric ribs are strong and angular, as in 

 most species of Gouldia, to which the species, when young, bears a great resem- 

 blance ; on the greater convexity of the sides of the shell the ribs gradually 

 decrease in thickness, but increase in number ; they remain tolerably distinct on the 

 anterior part of the shell, on the posterior they, however, soon disappear altogether, 

 and are replaced by mere fine strife of growth. 



Locality. — Ninnyoor, in white limestone ; not common. 



Formation. — Arrialoor group. 



