19S CHETACEOrS PELECYPODA 



observed ; these ribs are especially prominent on tbe anterior portion of the shell 

 in front of the unibonal ridge, but behind it on the areal portion only the smaller 

 close set strise prevail. 



The area itself is large, long, margined by a low ridge (see figs, 4 a and 6 cj, 

 and prominent along the median line, that is, where the edges of the two valves 

 meet. The lunule is broadly oval, somewhat deep, and below margined by an 

 impressed line, more or less interrupted by the striae of growth. The nymphse 

 are very strong and prominent. 



The hinge is perfectly similar to that of Cyprina islandica. In the right 

 valve there is one but slightly furrowed posterior cardinal, and two anterior 

 cardinals one above the other connected by reciprocally issuing projections, and 

 each of them is anteriorly somewhat prolonged. The left valve has also three 

 cardinal teeth, the posterior is the thinnest and elongated, the middle is slightly 

 prolonged, and the anterior is sub-triangular with a small inferior pit ; the upper 

 end of the anterior tooth is connected with the base of the middle one by an 

 oblique low ridge. The posterior lateral teeth are in both valves strong and 

 elongated ; the muscular impressions deep. 



The form and ornamentation readily distinguished this species from others. 

 The perfect identity of the hinge-teeth with those of the recent Cyp. islandica is a 

 very interesting fact. 



Localities. — Alundanapooram, Serdamungalum, east of Anapaudy, Koloture, 

 &c., in ferruginous or greyish highly calcareous sandstone ; common. 



Formation. — Trichinopoly group, for which the present species seems to be a 

 characteristic fossil. 



2. Cyprina cristata, Stoliczka, PI. IX, Fig. 1. 



Cyp. testa sub-qtiadrangulari, alta, carina acutissima ah umbonibus ad termina- 

 tionem itifero-jyosteriorem decurrente instructa, sub umbonibus emargiuata et infra 

 emarginationem paxdo producta ac rotundata ; superjicie antice lamellis crassis dis- 

 tantibtis concentrice ctirvatis ornata, ad utrumque lattis carina; IcBoigata ; liimda 

 prirva, transversaliter ovulata, non excavata, infra linea duplici mai^ginata. 



Height : length of shell ... ... ... ... 0-87 



Thickness : „ „ ... ... ... ... 0-50 



The only specimen known is the one represented in Plate ix. I have not been 

 able to obtain a view of the hinge-teeth, but from the external great similarity with 

 C. Forbesiana I presume that it is also a Cyp)rina. However, it is possible that 

 it belongs to the sub-genus Cicatrea, for on close examination I found that the 

 fulcra are not prominent, as noted in fig. 1 c, but I cannot see a double groove for 

 the ligament ; thus the generic determination requires confirmation. It is readily 

 distinguished from the former species by being less inflated, much higher in 

 proportion to its length, with the unibonal carina much stronger and sharper, 



