432 NEW GENUS AND SOME NEW SPECIES 



Hab. Ohio. T. G. Lea. 



My Cabinet. 



Cabinet of T. G. Lea. 



Cabinet of Prof. Vanuxem. 



Cabinet of P. H. Nicklin. 



Cabinet of the Academy of Natural Sciences. 



Diam. -8, Length 1*3, Breadth 2-2 inches. 



Shell ovate-elliptical, remarkably flattened over the ura- 

 bones from the beak to the basal margin, which frequently 

 causes the greatest diameter to be near to the anterior margin ; 

 substance of the shell thick ; beaks slightly prominent and de- 

 corticated ; ligament deeply seated, scarcely appearing above 

 the margin of the shell ; epidermis wrinkled, yellowish brown, 

 with transversely interrupted rays passing from the beaks in 

 a slight curve to the margin along the umbonial slope ; these 

 rays are hair like, undulated, and interrupted; cardinal 

 teeth very small and lobed ; lateral tooth remarkably thick 

 and situated on a large massive plate ; curve very slight and 

 directed much over the cardinal tooth, somewhat rough, up- 

 per division smaller than the lower ; anterior and posterior 

 cicatrices both distinct ; the smaller posterior cicatrix is situ- 

 ated against the end of the plate at the point of the divi- 

 sion of the tooth; dorsal cicatrices situated on the under part 

 of the cardinal tooth, perceptible; cavity of the shell very 

 small and irregularly waved; an indistinct depressed line 

 may always be seen to pass from the great posterior cicatrix 

 along the base of the lateral tooth into the cavity of the beaks ; 

 nacre white. 



Remarks. — This shell is peculiar in the massive plate on 

 which is situated its short and thick lateral tooth, as well as 

 in the very small size of its cardinal tooth. It has scarcely 

 any cavity under the beaks, the shell being very thick. Its 

 epidermal rays, in perfect specimens, are very unusual to this 

 genus ; in old specimens they are almost or quite obsolete. 

 It is remarkable also in its flat umbones. It resembles most 

 in form the gibbosus of Barnes, but is less rostrated and more 



