No. 275.] 
4. L. oblonga. — Shell oblong, sides nearly straight and parallel, regu- 
larly arcuated above, and abruptly rounded at base. Length, I inch. 
Locality^ Martville, Cayuga county, in sandstone. 
Atrypa. 
A. elongata. Shell narrow elliptical, with numerous radiating striae; 
lateral margins truncated in the middle; inferior valve gibbous in the 
middle, and somewhat depressed on the sides. Length, 3 inches. X/?- 
calitt/y Helderberg, in sandstone. 
Delthyris. 
1. D. acuminata. Shell subcordate, dilated transversely; valves with 
radiating sulci; superior valve, very prominent and carinated in the mid- 
dle, carina not sulcated, slightly arcuate in length; lateral extremities 
rounded; base emarginate; inferior valve profoundly bilobed, sulci not 
deeply impressed; beaks approximate. Length 21 inches. Locality, 
Helderberg, in limestone. It resembles Atrypa acuminata, (Sow.) 
2. D. granulosa. Shell trigonal, ventricose, with very numerous mi- 
nute elevated punctae; ribs numerous, convex, the interstices not deep- 
ly impressed; inferior valve bilobed; beak elevated, incurved, foramen 
large; superior valve with a wide medeal convex depressed rib, with a 
narrow groove down the middle; umbo prominent, summit rounded. 
Length II inches. Locality: uncertain, but belongs to the shales of 
No. 7. 
3. D. arenosa. Shell trigonal, with radiating sulci; superior valve with 
a rounded elevation in the middle, having about 4 sulci upon it, or 5 
ribs; inferior valve, with a corresponding furrow; basal margin undula- 
ted, prominent and angulated in the middle. Length 2k inches. La- 
caliiy, Helderberg, in sandstone. 
Fresh Water Shells, 
Cyclostoma. 
C pervetusta. Shell orbiculato-conical; volutions 3 or 4; base with a 
profound umbilicus, exhibiting the volutions to the apex. Length 
J inch.. 
Planorbis. 
P. trilobaius. Shell orbicular, with three nearly equal rounded pro 
minent lobes; the large volution rapidly enlarging towards the aperture. 
Length \ inch. 
[Assem. No. 275.J 9 ,4 
