14 



lating, concentric striae cross the radiating folds in well 

 preserved specimens. 



Length from '12b to '20 of an inch. 



Locality. — Spergen Hill. 



/./fcoNOCARDiUM carinatum. — Shell subtrigonal, gibbous in 

 the middle, anterior end cordate ; hinge line straight ; beaks 

 very small, strongly incurved, rising little above the hinge 

 line ; posterior side straight above, sloping upwards from 

 below, and gradually tapering to the extremity, faintly con- 

 stricted at its junction with the body of the shell and gap- 

 ing below ; hiatus elongate-lanceolate, crenulate ; umbonial 

 slope strongly carinated ; carina reaching from beak to base 

 where it is strongly salient ; anterior side obliquely truncate, 

 and abruptly produced into a small conical tubular exten- 

 sion of the hinge line. Surface marked by simple radiating 

 ribs and extremely fine concentric strise, which in passing 

 over the ribs give the surface a granulated appearance. On 

 the anterior slope the ribs are finer and closer than on the 

 sides of the shell, and strongly curved. 



Length, from '20 to *33 of an inch. 



Locality. — Bloomington and Spergen Hill, la. 

 I Conocardium cuneatum. — Shell sub-trigonal or abruptly 

 clavate ; hinge line straight; beaks anchylosed, incurved, 

 very small, rising but little above the hinge line ; umbonial 

 slope angular ; anterior side truncate, concave just within 

 the angle of the umbonial slope, convex in the middle, and 

 abruptly produced above, in continuation of the hinge line, 

 in a tubular wing ; posterior side vertically compressed, 

 straight along the hinge line, and abruptly declining at the 

 extremity, sloping along the base from the centre of the 

 shell to the extremity. Hiatus elongate, extending forward 

 to near the middle of the shell, rounded and expanded at 

 the posterior extremity, and deeply crenulate in the margins 

 of the narrower part. Surface marked by distinct radiating 

 costae, which often alternate in size or bifurcate on the pos- 



