MARYLAND GEOLOGICAL SURVEY 671 



tinguishable upon the casts; the anterior ones more strongly impressed. 

 Each valve with a strong, somewhat curved cardinal tooth beneath the 

 beak, with a pit for the reception of the tooth of the opposite valve ; in each 

 valve is a single anterior and posterior, rather strong, lateral tooth, some- 

 what remote but nearly equidistant from the cardinal tooth. The inner 

 free margin of the valves is crenate. Externally the shell is marked by 

 flat, radiating costs wider than the interspaces; from the interspaces rise 

 rows of laterally compressed spinules or tubercles which are longer and 

 stronger upon the anterior and posterior slopes towards the hinge extrem- 

 ities ; 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 of the shell the rows of larger 

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

 between the larger ones. 



" This species is by far the commonest and most widely distributed 

 Cardium in the Cretaceous faunas of Xew Jersey. It exhibits considerable 

 variation, especially in the straightness of the posterior margin of the 

 shell and in the prominence of the postero-basal extremity, but the casts 

 can almost always be easily recognized by the strong convexity or gib- 

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

 anterior. The surface markings of the shell most closely resemble those 

 of G. dumosum, but the radiating costfe are comparatively broader and 

 natter with narrower interspaces, and consequently the spines upon the 

 surface are more compressed laterally. C. dumosum 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 of 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. multi- 

 radiatum, or to G. eufalense. Whitfield has apparently illustrated dif- 



