OP SOUTHERN INDIA. 467 



costis acutis, siniplicibus cmt dichotomis, interspatiis fere cequaUbns separatis, concen- 

 trice minute striolatis, in latere dorsali scspissime fortioribus, ad marginem crasse 

 dentatis, deutibus in margine ventrali nonnunquam sub-obsoletis vel minoribus ; area 

 ligamentali late triangulata, medio leviter impressa ; valva supera ad apicem scspe 

 abbreviata aut trtmcata ; impress, muse, late ovata, excentrica, ventrali, sub-mar- 

 ginali ; impress. palliaU Icevi, scepe indistincta. 



The great variations in form of this species are well known, though generally 

 a more or less ovate shape is traceable. The valves are sometimes almost equal, 

 but usually the upper one is somewhat less elevated, the ventral margin is in both 

 near the beak usually somewhat expanded. The development of the ribs depends 

 upon the amount of attachment of the lower valve, and where the ribs are wanting 

 on this one they are equally so on the other valve. On the free portions of the 

 valves the ribs are, however, always well marked, sharp, about equidistant, single 

 or dichotom, and very often nearly of equal strength ; only occasionally one or two 

 of the median ribs become much stronger than the others. The margins are 

 dentated according to the size of the ribs ; on the ventral side the dentation is 

 generally less strong than on the dorsal one. The ligamental area is large, sub- 

 triangular; the beak is in the lower valve generally entire, sometimes slightly 

 curved ; in the upper the cardinal edge is generally truncate, and the ligamental 

 area, therefore, shorter, and in the middle also less excavated. 



I can see no essential difference between Indian specimens and those from 

 various parts of Em-ope. Coquand (Monog. Ostr. cret., p. 87,) identified Forbes' 

 O. pes-leonis with O. Deshayesi, Fischer, but this last species differs apparently 

 by having the ribs less sharp and the muscular impression more removed from 

 the umbones. 



Localities. — Anapaudy and Serdamungalum (in brownish calcareous sandstone, 

 Trichinopoly group), Moraviatoor, Odium, Ootatoor, (in earthy limestone, Ootatoor 

 group). 



Formations. — Trichinopoly and Ootatoor groups. 



In Europe this species occurs in the middle cx*etaceous series (Carentonien 

 and BotomagienJ ; it is one of the most common species all through Germany and 

 France, and is also reported by Eichwald from Daghestan. 



2. OsTKEA [Alectrtonia] cupelloides, Stoliczka, PL XLVI, Fig. 4. 



Ost. \_Alectr.'] valva inferiore cupelliforme, sub-rotundata, tenni, ad umbonem 

 late affixa, radiatim costata, costis modice elevatis, cequidistantibus, striis incre- 

 menti tenuissimis ac confei'tissimis tectis, ad marginem undique obsoletis ; area 

 ligamentali medio latiuscula et modice excavata ; impress, musculari ventrali, 

 excentrica, indistincta; imp. palliali plicosa, sub-marginali. 



Locality. — Near Arrialoor, in whitish sandstone. 

 Formation. — Arrialoor group. 



