468 CEETACEOUS PELECYPODA 



I liavc not seen more than the figured lower valve of this remarkable species. 

 The radiating ribs all become obsolete near the margin and the pallial impression is 

 crenulated in its entire extent, which character readily distinguishes this species 

 from any others reported from cretaceous deposits. 



3. OsTREA [Alectryonia] amorpha, Soioerhy, PI. XLVIII, Fig. 3. 



1846. Ostrea amorpha, Sow., apud Forbes, Trans. Geol. Soc, Lond., vii, p. 157, pi. 15, fig. 24r—eadem 



auctorum. 



Ostr. [Alectr.] testa irregulariter suh-rotundata, convexiuscula, crassa, radlatim 

 iiKsqualiter costata : costis ad marginem plicis nonnidlis concentricls intersectis. 



I have unfortunately very little to add to the meagre description of this 

 problematic species. The only specimen in our collection is very imperfect, but 

 it indicates a species allied to 0. Desori, Coq., (Monog. Ostr. cret., 1869, p. 117), 

 and may be identical with it. The geological position of both also coiTesponds, 

 Desori being from the Carentonien. Forbes' figure is based upon a very insuffi- 

 cient fragment, exhibiting the interior of it ; it is the only one that I could find 

 amongst Forbes' originals. 



Locality. — Near Serdamungalum, in bluish grey sandstone. 



Formation. — Trichinopoly group. 



4. Ostrea [Alectryonia] carinata, Lamarck, PI. XLVIII, Fig. 5 ; PI. XLIX, 



Figs. 1—2. 



1810. Ostrea carinata,'La.m., Ann. d. Museum, viii, p. 166; — eadem Coquand, Monog. Ostr. cret., 1866, 

 p. 129, cum synon. 



O. [Alectr.l testa elongata, angusta, curcata, cequivalvi ; valcis costis numerosis 

 ad medium complicatis, et irregulariter dichotomis, sub-rugosis, in latere aiitico, 

 concavo, simplicibiis, in latere convexo ahrupte descendentibus, supra ad marginem 

 elevatiuscidis, nonnunquam duabtis vel tribtis seriebus tuberctdorum coi'onatis ornatis ; 

 auriciiUs parvis, aid sub-a^qualibus, ant sub-obsoletis ; nmbonibus scepissime paido 

 incurvatis ; Ugamentum in fovea ampla valmdce dextrce, jugo valv. sinist. congruente, 

 situm ; impressione muse, ovate elongata, prope marginem cardinalem posita ; margiue 

 interiore valvarum undiqiie acute dentato. 



Shell generally moderately curved, always very narrow, but often growing 

 to a very considerable thickness. The ribs are numerous and sharp, ii-regularly 

 dichotomous, somewhat more raised on the upper convex than on the concave 

 edo-e and occasionally ornamented with two or three rows of tubercles. The 

 maro'ins of both valves are very strongly dentatcd. The beaks are depressed and 

 "cuerally slightly twisted, the auricles being cither developed of small size, or 

 nearly obsolete. On the anterior portion of the concave side the ribs are always 

 simple, slightly curved, very much resembling those of O. ungulata. The liga- 

 ment of the right valve is lodged in a deep groove Avhich corresponds to a flattened 



