LAMELLIBRANCHIATA OF THE LOWER MARLS. 115 



near the posterior cardinal margin are sliarp and very slightly crenulated. 

 The ribs are coarse and distant on the anterior and middle parts of the shell, 

 but gradually become finer and more closely arranged toward the posterior 

 part. Interspaces concave. No postero-cardinal area is visible on the 

 specimen used, the ribs apparently passing, without interruption, across the 

 entire disk of the shell and terminating on the cardinal margin. The ribs 

 of the anterior end curve strongly forward in passing to the basal and ante- 

 rior margins, while those of the hinder parts of the valve pass more directly 

 across to the postero-basal margin. 



This species differs from any of the others described from these beds 

 in its form, but more particularly in the style and number of the surface 

 ribs. They are more numerous than on any of the other forms, there hav- 

 ing been about twenty-three on the specimen figured, which is only one 

 inch and an eighth in length. Their flattened surface and the gradual in- 

 crease backward is also the opposite from that which is seen to occur on 

 those. In form it would correspond to the group Pectinata, and in the style 

 of the ribs resembles T, pectinata Lam., except that the increase in number 

 and size of ribs is directly opposite from what it is in that species. 



Formation and locality. — In coarse olive green indurated marl at the 

 deep cut on the Holmdel and Keyport turnpike, Monmouth County, New 

 Jersey, at the base of the Lower Marls. The substance of the shell is en- 

 tirely changed to Vivianite, which is soft and of a bright blue color, very 

 easily destroyed by handling or rubbing. 



Order SIPHONIDA. 



Suborder INTEGRIPALLLATA. 



CRASSATELLID^. 

 Genus CRASSATELLA Lam. 



In the Proceedings of the Academy of Natural Sciences of Philadelphia, 

 1872, p. 50, Mr. Conrad refers back to the American Journal of Conchology, 

 Vol. V, p. 47, where he describes a new genus Pachythoerus for the recep- 

 tion of all the Cretaceous, Eocene, and Oligocene CrassateUas which he con- 

 siders as generically, or at least subgenerically, distinct from the Miocene 



