on a New Genus of Shells from Nebraska. 35 
ing of other differences, the fact that the open extremity of the 
horse-shoe shaped muscular scar in our shells is always turned 
towards the shorter end, or in other words, that the apex is 
— in front of the middle instead of behind it, shows they 
ave no affinities to that or any allied genus. , 
They would then seem to be perhaps more nearly related to 
Acmea and Gadinia than to any other of our existing moliusca, 
since in both these genera the animal is more or less unsymmet- 
rical, the former having the branchial plume exserted from the 
right side of the neck, and the latter a siphon occupying a groove 
on the right just in front of the anterior extremity o 
cular scar, which is shorter on that side than on the other. Our 
shells, however, differ from these genera in the peculiar attenu- 
ate or interrupted character of the muscular impression on the 
right posterior side, and the folding back of the-apex.* In the. 
thinness of the shell and the nature of the surface, they are 
EOLUS, 
- PATELLIFORMIS, (= Helewum patel 
Washington, D. C., Nov. 20, 1859. 
* Dr. A. A. Gould, the well known conchologist of Boston, to whom we sent 
sketches of these shells, writes that he concurs'‘with us in regarding them as being 
— distinet from all the recent genera to which such fossil forms are usually 
erred, 
