296 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. sulcifera, 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. sulcifera 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. 



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



Formation. — Arrialoor group. 



2. CuASSATELLA ZiTTELiANA, StoUczJca, PL V, Eigs. 15-19. 



Cr. testa cuneiforms elongata^ incequilaterali^ tumida, ad margmem Itmularem 

 emarginata^ antics breviter rotundata^ postics attsnuata^ suh-caudata st oblique 

 truncata, carina acuta ab umbonibus ad tsrminationsm postero-inferiorem decurrents 

 instructa, concsntries costulata^ costulis in regions umbonali crassis, psriphsriam vsrsus 

 tsnuioribus, confsrtis^ postics fsrs omfiino obsoletis ; lunula slongato ovali, profunda^ 

 Icevigata, margins acuto circumscripta ; area longiors, angusta stiamqus profunda. 

 Cardins dsntibus cardinalibus anterioribus in utraqus valva st fossa cartilaginigsra 

 postica msdiocritsr sxcavata instructo, dsnts antico in valva dsxtra laterali approxi- 

 mator postico fsrs omnino obsolsto ; in valva sinistra dsnts laterali antico parvulo^ 

 postico elongato, distinctiore. 



H eight of shell : its length ... ... .^. _, 9-74 



Thickness „ : „ ... ... ... __ 0'64 



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

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

 SedgwicMa. 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 striae of growth. 



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



Formation. — Arrialoor group. 



