OF SOUTHERN INDIA. 157 



15. Cijimmeria, Conrad, 1864, (Proc. Ac. Nat. Sc, Phil, 1864, p. 212). Shell 

 sub-orbicular, of moderate thickness, with the valves more or less compressed, 

 concentrically striated, rarely with radiating strice ; pallial sinus small and obtuse, 

 or distinctly angular and deep ; hinge in the right valve with two diverging pairs 

 of thin laminar cardinal teeth, each pair originating from one point, and thus 

 preserving the character of a single bifid tooth, left valve with three cardinal 

 teeth, the first and second are slightly diverging, and both strongly compressed, 

 the anterior being the thinner one, the posterior tooth is parallel to and separated 

 only by a shallow groove from the very thick fulcrum; lunula not much or 

 not at all impressed, but beaks pointed and approximated. None of the species 

 that I have examined possessed a regularly margiAcd lunula. There is on the 

 dental area of the hinge a distinct impression below the lunula of both valves, and 

 if observed in one only, it may give rise to a supposition that this pit corresponds 

 to a tooth in the other valve, but that is certainly not the case in any of the 

 species of which I have been able to examine both valves ; and judging from 

 analogy, it is not likely to be the case in others which are believed to possess 

 it. And should it really be the case in any of them, those species must be 

 referred to Dosin'm proper, as the type of the present genus is considered to be 

 Cyprhnma excavata, Morton. 



This is a very well marked type of cretaceous shells, belonging to the 

 DOSiNiiN^, as shown by the general character and especially the dentition of the 

 hinge, and not to the Tellinid^* in which family it is classed by Conrad. The 

 genus is equally well separated from Gemma, and appears as yet to have been 

 found in cretaceous deposits only. I shall enumerate further on the cretaceous 

 species which have been described under different genera, as partially pointed 

 out by Conrad (Am. Journ. Conch., ii, p. 102). Many of the fossil LucincB and 

 Astarte may prove to be Cyprmierice. The genus also occurs .in the eocene of 

 Sind and other parts of India. 



16. Cyclina, Deshayes, 1849, (vide Deshayes in his list of Conchifera 

 in the British Museum, 1853, p. 29). Shell sub-orbicular, thin, concentrically 

 or radiately striated, hinge with three cardinal, diverging teeth in each valve, the 

 most anterior of the right valve sometimes obsolete or nearly so ; pallial sinus 

 triangular, generally ascending. Type, Venus Chinensis, Chemn. Deshayes 

 (loc. cit.) describes twelve recent species, all of which do not, however, appear to 

 belong to this genus. Some are identical with known forms, but a few others 

 have been described since. 



The thin structm-e and dentition readily distinguish this genus from Dosinia, 

 or any of the other genera mentioned. The genus is known to occur in tertiary, 

 but as yet not from older deposits, for Zittel's Cyclina primcEva is a Cyprimeria. 



17. dementia, Gray, 1840.t Shell elongately ovate, tumid, very thin, covered 

 Avith epidermis, pallial and muscular impressions faint, pallial sinus narrow, 



* Some species particularly have a remarkably great external resemblance to Arcopagia, having also been described 

 as such by d'Orbigny. 



t Vide Malacoz, Blotter, vol. xvi, p. 190. 



2q 



