216 PALEONTOLOGY OF NEW JEESEY. 



hinge stiaicture, or other generic features. In its general appearance it 

 very closely resembles F. trapezoidea Conrad, and I am extremely doubtful 

 of their specific difference. But that one I only know from a single crushed 

 cast \yhich represents more properly the exterior, while these are strictly 

 internal casts. The only differences which I can see are, that this form is a 

 little shorter and much more ventricose, with, perhaps, larger beaks. 



Formation and locality,— In the Green Marls in Burlington County, New 

 Jersey, according to Mr. Conrad. The specimen figured is Mr. Conrad's 

 type, and is borrowed from the collection of the Academy jf Natural Sci- 

 ences, Philadelphia. Other specimens, having the same lithological char- 

 acters precisely, in the collection at Rutgers College, are from the lower 

 layers of the Upper Marls, below the Eocene layers, and it is probable that 

 the above example is also from the same horizon. 



PETRICOLID^. 



Genus PETEICOLA Lam. 



Petricola Nova-^gyptica, n. sp. 



Plate XXVIII) Fig. 22. 



A single cast of a right valve of this species has fallen under my no- 

 tice. It indicates a shell of only medium size, and proportionally broad 

 from the hinge to the basal margin, with moderately large but not promi- 

 nent beaks, which have been situated near the anterior end and are directed 

 anteriorly, and which do not rise much above the cardinal line. The shell 

 has been widest anteriorly, and narrows moderately toward the posterior 

 end, which, although the cast is somewhat imperfect at this part, shows it 

 to have been about three-fourths as wide as the anterior, and more narrowly 

 rounded. The cast shows no evidence of surface markings on the shell 

 other than irregular concentric undulations; although, from the distinctness 

 of the marginal line anteriorly, it would appear to have been considerably 

 thickened. The posterior muscular scar on the cast is small, moderately 

 distinct and elongated in the direction of its advancement during the growth 



