OF DENISON UNIVERSITY. 
8l 
cave, and finely striate. About twelve of the ribs are found on a 
shell of moderate size. Greatest convexity above the middle. 
Length. 
Height. 
Be’k fr’m 
anterior. 
Heig’t at 
from post. 
Width. 
Number of 
ribs. 
Length to 
height. 
23 
12 
7 
10 
8 (?) 
12 
2-1 
24 
14 
12 
12 
1. 7-1 
22 
1 1 
7 
10 
5-6 (?) 
1 1-12 
2-1 
16 
8 
5 
7 
— 
10 
2-1 
18 
10 
5 
9 
10 
i.8-[ 
21 
12 
6 
10 
12 
1 . 7-1 
1 1 
6.5 
3 
5*5 . 
4 
6-8 
1. 6-1 
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. 
Yar. 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 3.3 high and had but five or six costae. 
Yar. elegantula 
does not differ in proportions or hinge structure, but 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. 
Yar. allorisiniforjYhis 
has the beaks a little, farther forward and the intermediate striolations 
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 possess. Neverthe- 
less, specimens of the present species, which failed to exhibit the teeth, 
were regarded by Prof. Winchell as Cardinia concentrica. Either 
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- 
