MOLLUSCA. 593 



anterior and posterior slopes towards the hinge extremities; on 

 the central portion of the shell each third row of processes is 

 more conspicuous than the two intervening rows, the spines 

 being^ longer and larger, one of them occupying the space of 

 two or three of the smaller ones of the intervening rows, the 

 smaller ones sometimes being scarcely more than tubercles but 

 little elevated above the surface of the ribs of the shell ; upon the 

 anterior and posterior slopes o<f the shell the rows of larger 

 and smaller spines alternate, there being but a single row of 

 smaller spines between the larger ones. 



Remarks. This species is by far the commonest and most 

 widely distributed Cardiwm in the Cretaceous faunas of New 

 Jersey. It exhibits considerable variation, especially in the 

 straightness of the posterior margin of the shell and in the prom- 

 inence of the postero-basal extremity, but the casts can almost 

 always be easily recognized by the strong convexity or gibbosity 

 of the valves, and the abrupt posterior slope as compared with 

 the anterior. The surface markings of the shell most closely 

 resemble those of C. duwiosum, but the radiating costae are com- 

 paratively broader and flatter with narrower interspaces, and 

 consequently the spines upon the surface are more compressed 

 laterally. C. dumoswm is also more nearly equilateral, with less 

 convex valves than this species, and does not attain so large a 

 size. 



It has been a matter o>f much difficulty to determine to what 

 species this common shell should be referred. Previous to the 

 publication of Whitfield's monograph, it seems usually to have 

 been referred to* C. muJtiradiatum or to C. ewfcmlensi-s. Whit- 

 field has apparently illustrated different individual internal casts 

 of the species under four different specific heads. His figures 

 1 8 and 19 of C. eufawlensis represent a more than usually gib- 

 bous cast O'f this species, the true C. eufaulensis being a funda- 

 mentally different shell without the spines rising from the inter- 

 spaces between the ribs and consequently not even a member of 

 the sub-genus Criocardium. Whitfield's figures 10 and n of 

 C. dumosum represent a more than usually rounded form of the 

 species under discussion, the specimen is larger, more convex and 

 38 PAI, 



