OF SOUTIIEHN INDIA. 291 



difobus crassis diver gentibus, antico brevi, postico valde elongato, in valca sinistra 

 dente mediano parvulo, postioo tenui et elongato instructo. 



Height of sheU : its length ... ... ... 0-84 - 0-86 



Thickness „ : „ ... ... ... 0-77 - O'SO 



Although approaching to an orbicular form, this species is always a little 

 longer as compared with its height. The ribs when well preserved are tricarinate, 

 sej)arated by very deep sulci. In each rib the median portion is the most pro- 

 minent and ornamented with sharp laterally compressed tubercles. The lateral 

 ridges appear to be nearly smooth ; they are in some specimens more strongly 

 developed than in others; there is, however, also on these a fine crenulation to l)e 

 observed. Again, in some other specimens, particulai'ly those of smaller size, the 

 lateral ridges are nearly obsolete (see fig. 15), and the intermediate sulci are then 

 considerably increased in width. If in such specimens the tubercles become worn 

 off, they attain a rather different aspect from that they originally possessed; such 

 worn specimens had been figured by Forbes as Card, orbicularis, and as Card. 

 Jaquinoti by d'Orbigny. 



I am not quite certain about the identification of Forbes' Cardita striata, but 

 I have no other species from the South Indian cretaceous rocks to compare with it. 

 Upon examining Forbes' original in the collection of the Geological Society of 

 London, I found it much broken on the upper and posterior margins. The form and 

 convexity of the shell and the number of ribs are in both (it and orbicularisj the 

 same ; the surface is in the former much worn down, but the radiating strife on the 

 ribs are tolerably distinct. I found in our specimens of orbicularis that, when the 

 median portions of the ribs with their tubercles break off, this portion becomes 

 bipartite, and thus with the addition of the lateral ridges each rib becomes quadri- 

 partite. I regard the specimen described under the name of C. striata as a form 

 of orbicidlaris in this altered stage. At least, unless proved by the discovery 

 of better materials, it seems impossible to form any other conclusion. 



The hinge of the right valve of Jaquinoti has two unequal diverging cardinal 

 teeth ; the anterior is shorter than the posterioi", and both are of considerable thick- 

 ness ; in the left valve there is a small tubercular median cardinal and a much 

 elongated, rather thin, posterior cardinal tooth. This dentition corresponds well 

 with that of typical Cardita and not with Cardium, to which genus d'Orbigny 

 referred the species. 



Locality. — Ninnyoor, in white or brownish limestone ; not uncommon. 



Formation. — Arrialoor group. 



XXIX. Family,— CRASS A TELLIByF. 



The animals have the mantle margins disunited, entire or finely cirrated at the 

 edges, especially posteriorly ; the foot is sub-triangular, compressed ; the gills rounded 

 in front, pointed posteriorly and produced, reaching below the posterior muscular 

 scar ; there are two sub-equal leaflets on each side, the outer smaller than the inner ; 

 the palpi are sub-triangular, of moderate size, pointed behind. 



4 B 



