NATURAL SCIENCES OP PHILADELPHIA. 325 



larly rounded from the middle to the anterior extremity of the hinge line. 

 Anal margin, lower third, at about a right angle to the basal edge, upper portion 

 curved as it passes the muscular scars, and straight, inclined anteriorly be- 

 yond, until it reaches the hinge line. Hinges composed of the characteristic 

 teeth, but very robust. Anterior muscular scars very deep, posterior, bardly 

 visible. 



Length 1-6 in. Width 1-9. Transverse diameter 1-5 in. 



Locality, Boonton, N. J. My collection, from Mr. Abbott. 



There is a specimen in the collection of the Academy, apparently belonging 

 to this species. Both are casts. The Academy's specimen, however, hasalitho- 

 Jogical character, entirely unknown to me, in the Cretaceous. It is from a light 

 grey calcareous clay rock. I have been unable to see the impression of the hinge 

 in that specimen. Mine shows the impressions of all of the cardinal teeth per- 

 fectly. There can be no doubt of the difference between this genus and Oyprina, 

 to which it was referred by d'Orbigny. Dr. Morton's figure of the hinge (Synopsis, 

 pi. 8) is correct for the right valve. That of the left valve is totally wrong. 

 An examination of the figure will suffice to show that the two valves, as there 

 represented, would not articulate. I have before me a drawing, which I made 

 from the original specimen, in the collection of the Academy. Anteriorly, 

 there is a large, flattened tooth, arising gradually in advance and ending ab- 

 ruptly, which articulated with the fosset, in advance of the two small, round 

 teeth in the right valve. These, in turn, correspond to two small fossets on 

 the left side. Behind these fossets there is a large, triangular pyramidal 

 tooth, matching the fosset in the right valve (not well represented) between 

 the two small and the long, narrow cardinal teeth ; the latter is received in 

 the left valve, between the pyramidal tooth and a corresponding tooth. There 

 is also a long, lamellar, lateral tooth, placed posteriorly, but represented too 

 near the edge in the figure of the left vale. The two figures in Dr. Morton's 

 illustration were apparently taken from the right valve. 



The present species is the most abrupt yet described. It is nearest 

 V. Conradi, but differs in being higher, the beaks even more anterior ; the 

 basal margin straighter, the posterior edge by far less prominent and the 

 transverse diameter proportionally much greater. From the cast, the surface 

 does not seem to have possessed varices. It resembles, on its posterior face, 

 some of the forms of Cucullcea vulgaris, but can be distinguished from that 

 species by wanting the internal plates, and by the hinge being composed of a 

 few very robust teeth. 



Akca Lam. 



A. altirostris. Small, robust, elongated, subquadrate. Beaks a little 

 in advance of the centre, very prominent, distant and somewhat incurved. 

 Basal margin regularly convex, posterior edge nearly straight, and most promi- 

 nent at its lower portion. Surface markings unknown, a faint umbonal ridge 

 extending from the beaks to the margin. Muscular scars distinct, but not 

 prominent, posterior ones largest and most regular in shape. Pallial impres- 

 sion well marked. Hinge line curved on its inner margin. 



Length, -55 in. Width, -65 in. Diameter, -4 in. 



Of nearly the same size as Cibota muUiradiata, nobis, this species can be 

 distinguished by the very prominent beaks, and less regularly gibbous form. 

 The margin, which, in that species, is crenulated, does not seem to be in this, 

 from an examination of the cast. The basal margin is closed in this species, 

 and gaping in that. 



It is more nearly related to A. quindecemradiata, but is much smaller, the 

 beaks are much more prominent, proportionally, and it wants the distinct 

 radiating lines, plainly visible on the casts of that species. 



Locality, Crosswicks, N. J. My collection, from Dr. Slack. 



1861.] 



