18 



extremity ; beak nearer the anterior end, small ; posterior 

 umbonial slope extremely gibbous (a broad undefined ridge) 

 reaching to the base of the truncation. Surface marked by 

 fine regular concentric lines parallel to the border of the 

 shell. 



Length, * 11 to * 13, width *08 to *10 of an inch. 

 Locality. — Spergen Hill. 



Cypeicardella oblonga. — Shell oblong, sub-quadrangu- 

 lar ; anterior end narrow, rounded; posterior end broader, 

 flattened, and almost vertically truncate ; cardinal margin 

 nearly straight and horizontal behind, declining in front; 

 base nearly parallel to the hinge line ; beaks small, somewhat 

 prominent, gibbous below ; posterior umbonial slope gib- 

 bous or sub-angular, and extending obliquely downwards 

 and backwards to the base of the truncation ; lunule small, 

 ovate, deep in the centre ; escutcheon linear, distinct. 



Length, -09 to '30, width '06 to '20 of an inch. 



Locality. — Spergen Hill ; Bloomington. 

 1/ Cypricardella plicata. — Shell oblong, sub-quadrate, 

 hinge line slightly arched, the base and hinge line nearly par- 

 allel ; gibbous in the middle above, and anteriorly, depressed 

 in the middle towards the base ; beaks near the anterior end, 

 small, and scarcely rising above the hinge margin ; anterior 

 end short, scarcely extending beyond the beak, rounded ; 

 posterior extremity doubly truncate ; a strong fold or an- 

 gulation extending from the umbo to the posterior basal 

 margin, and a smaller similar fold midway between that and 

 the hinge line, the intervals on the margin between these 

 being truncate. Surface marked with concentric lines of 

 growth. 



Length, '12, width '12 of an inch. 

 Locality. — Bloomington ; la. 



CYPKICARDIA, Lamarck. 



Cypricardia Indianensis. — Shell elongate-ovate, narrow 

 and rounded in front ; posterior end broader, somewhat com- 



