OP SOUTHEEN INDIA. 469 



ridge of tlie other valye. The muscular scars are situated very close to the hinge ; 

 they are of an elongately oval shape, the upper portion being usually covered up by 

 a thin lamina extending below from the hinge-margin. 



Localities. — Coonum (in a brownish calcareous rock, very common) ; south- 

 east of Veraghoor ; Odium, Poodoor, Moraviatoor, KuUay, &c., mostly in a brown- 

 ish limestone. 



Formations, — Trichinopoly and Ootatoor groups. The Indian specimens per- 

 fectly agree with those from Europe. The species does not generally grow to a 

 great length ; 120—150 m. m. being a large size, but these specimens have some- 

 times a great thickness. One specimen from KuUay in our collection is 150 m. m. 

 long and 80 m. m. high in the middle of the valves. 



O. carinata maintains in Europe a somewhat lower horizon than the two 

 following species ; exactly the same is the case in India. It is a characteristic 

 fossil of the middle series of cretaceous deposits f Carentonien and Botomagien 

 of Coquand). It has been noticed in these beds almost throughout Europe, in 

 Africa and in Asiatic Russia. 



5. OsTEEA [Alecteyonia] pectinata, Lamarck, PI. XLIX, Pigs. 1 — 2. 



1810. Ostrea pectinata, Lam., Ann. du Museum, viii, pi. lQ^,—eadem Coquand, Mon. Ostr. cret., 1869, p. 76, 

 cum synon. (O. frons, Park., et prionata, Goldf., et auctorum). 



O. [Alectr.~\ testa angusta, plus minusve curvata, cequivalvi, prope umbones 

 compressiuscula, auriculis incequalihus, aut bene distinctis aut sub-obsoletis, instructa, 

 auricula externa fseu posticaj breviore ; valvis costis radiantibus acutis rugulosis, 

 nonnunquam minute striolatis, ad medium simplicibus, deinde scepe dichotomis, Us in 

 margine convexo supra sub-spinulose elevatis, ad latus verticaliter descendentibus 

 ornatis ; margine valvarum undique crasse dentato ; impressione muscul. elongate 

 ovata, ad latus umbonale sub-acuta, marginali. 



The shape is in this species rather variable, some specimens are nearly 

 straight, others slightly curved, and again some so strongly bent that the termina- 

 tion almost touched the beaks. The ornamentation of the valves is peculiar, 

 the ribs being simple in the middle, mostly bifurcating at the sides, sloping 

 somewhat gradually on the concave side, but very abruptly on the convex one, 

 on the upper edge of which each rib is generally strongly elevated, occasionally 

 rising almost to a blunt spine. The ribs themselves are much thinner and more 

 numerous than in O. ungulata, but stronger and less numerous than in O. serrata 

 or in O. carinata. 



In the broadly attached specimens both the ears are generally well developed, 

 the one on the convex (or posterior) side being smaller than that on the concave 

 side. In other specimens which were attached only by a very small portion 

 of the valve the ears are usually less developed, the posterior one sometimes 

 quite obsolete, the anterior being externally ribbed. The ligamental grooves are 



5y 



