MOLLUSCA. 595 



mens being: height, 19 mm.; width, 21 mm.; convexity of one 

 valve, 9.5 mm. Anterior margin broadly rounded, passing regu- 

 larly into the moderately convex basal margin; postero-basal 

 extremity subangular; posterior margin obliquely subtruncate 

 or gently convex. Valves gibbous, most prominent along the 

 rounded or subangular umbonal ridge, the post-umbonal slope 

 abrupt, the anterior slope from the umbonal ridge convex ; beaks 

 rather small, incurved, directed anteriorly. Surface of the modi- 

 fied casts marked by rather fine radiating ribs. 



Remarks. This species is known only from the somewhat 

 modified internal casts upon which the actual surface features 

 of the shell are not preserved. The species can be distinguished 

 from all other members of the genus in the New Jersey faunas 

 by its comparatively small size, its low and broad form, and its 

 strongly ventricose or gibbous valves. 



Formation and locality. Merchantville clay-marl, Lenola 



(163). 

 Geographic distribution. New Jersey. 



Cardium knappi n. sp. 

 Plate LXVL, Figs. 4-7. 



Description. Shell wider than high, the dimensions of the 

 type specimen, an internal cast of a right valve, are: width, 37 

 mm.; height, 31 mm.; convexity, 12 mm.; length of hinge-line, 

 26 mm. Anterior margin broadly rounded, passing without 

 interruption into the still more broadly rounded basal margin; 

 postero-basal margin obtusely subangular, situated below the 

 mid-height of the valve; posterior margin obliquely subtruncate. 

 Umbo 1 prominent, beaks rather broad, the anterior and posterior 

 umbonal slopes subequal, muscular impressions of moderate 

 strength as seen in the casts. Surface markings not observed, 

 but the free margins of the cast are marked by crenulations 

 which are broadest along the posterior subtruncate margin, in- 

 dicating that the post-umbonal slope of the shell itself was 

 marked by moderately fine radial ribs, the central and anterior 

 portion of the surface being marked with still finer ribs. 



