OF DENISON UNIVERSITY 



Si 



cave, and finely striate. About twelve of the ribs are found on 

 shell of moderate size. Greatest convexity above the middle. 



Length, 



Height. 



12 



II 



S 

 10 

 12 



6.q 



Three varieties may be- recognized by the character of the stria- 

 tions and these seem to be independent of size and may be worthy of 

 specific distinction, though intermediate gradations connect them. 

 One variety. 



Vaj\ plicatella 



has coarse folds or ribs separated by wide intervals. A shell 13 mm. 

 long and 8 mm. high, has only eight costae. The youngest specimen 

 seen is only 5 mm. long and 3.=^ high and had but five or six costae. 



Var. eJedantulcv 



does not differ in proportions or hinge structure, l)ut a shell 14 mm. 

 long and 9 mm. high, has twenty costae. A larger specimen 29 mm. 

 long and 15 mm. high, has about 25 ribs. 



Var. aUorisiiuform is 



has the beaks a little, Hirther forward and the intermediate strioiations 

 are nearly equal to the costae, causing the shell to resemble allorisma. 

 This species has given us much trouble. All the varieties herein de- 

 scribed possess the hinge characters of Palaeoneilo, which Cardina con- 

 centrica is said by Winchell, emphatically, not to i)ossess. Neverthe- 

 less, specimens of the i)resent species, which Hailed to exhibit the teeth, 

 were regarded by Prof. Winchell as Cardinia concentrica. luther 

 there is a species in Michigan exactly like ours, but without the teeth 

 or in the examination of hundreds of specimens we have not hap- 



