LAMELLIBRANCHIATA OF THE LOWER MARLS. 97 



tlie horizontal portion, the bending being at an angle witliin ninety de- 

 grees, the denticles on the middle part of the hinge being small and 

 numerous. Muscular scars, as seen on the casts, strongly marked; the im- 

 pression of the ridge deep, strongly arched, and situated pretty well up on 

 the posterior slope; surface of the cast marked by rather strong vascular 

 lines. The outer margin of the cast is bordered by a strong keel, indicating 

 the great thickening of the valves along the pallial line. 



The internal casts of the species, the condition in which it is usually 

 recognized, are quite globose, with distant and highly projecting beaks; the 

 hinge-line being strongly curved in large specimens, and the strong projecting 

 keel extends around three sides, being broadest on tlie anterior. In these 

 casts there is seldom any evidence of the hinge structure preserved, and it 

 is rarely that we find specimens which give any clue to these parts of the 

 shell. A single large individual from Freehold, N. J., preserving the shell in 

 part, I was enabled to manipulate so as to get the impression of the teeth 

 on each end of the hinge, and to some extent the line of small teeth between 

 them. These sliow very decidedly the features of Idonearca as established 

 by Mr. Conrad. 



Among the specimens which I have referred to this species, there are 

 several from a white sandy layer from Holmdel, N. J., in the cabinet at 

 Rutgers College, which are labeled C. neglecta Gabb. There are others of 

 the same kind also from white sandy nodules occurring at the base of the 

 Lower Marl Bed at Marlborough, N. J., in Mr. Schanck's collection, bor- 

 rowed for this work. These specimens preserve the shell in most instances, 

 and furnish the features of the shell as given above. Mr. Gabb described 

 these as a distinct form under the name C. neglecta, but I can see no reason 

 for considering them as distinct from I. antrosa Morton. Of course their ap- 

 pearance is very different when the shell is retained from that presented by 

 the internal casts alone, and the hinge features are quite inconspicuous in 

 these small shells as compared with that shown to exist in the large specimen 

 figured. Still all the features are there, and it only needs the strengthening 

 of these by increase of growth to make them the same. 



Formation and locality. — Those preserving the shell, including those 

 marked Cuctdlcea neglecta by Mr. Gabb, are from nodules of white sandy 

 4418 MON 9 7 



