CHEMUNG GROUP. 
271 
There is considerable resemblance between this shell and the last, and they may prove to 
be varieties of one species, the hinge line more extended in the younger ones. 
Localities —Ithaca ; Cayuta creek ; Chemung. 
3. Delthyris mucronata? (See page 205, fig. 3.)—Transversely elongated; hinge line 
extended into mucronate points ; beak little elevated above the hinge line ; mesial sinus well 
defined, with a small rib in the bottom ; surface marked by about fourteen rounded, imbricated 
ribs on each side the mesial fold. 3 a , an enlarged portion of the shell. 
This fossil differs in no respect from the D. mucronata of the Hamilton group, except the 
rib in the centre of the mesial sinus. It is referred to this species, till more specimens have 
been examined. Locality , Troupsburgh, Steuben county. 
4. Delthyris inermis, n. s. — Semicircular ; beak of the lower valve much extended above 
the hinge line ; hinge line not extending beyond the shell; surface marked by about twenty- 
five equal, simple ribs on each side the mesial fold; mesial sinus deep and well defined, 
marked by about eight divaricating ribs, which are smaller than those on either side. 
This fossil is very abundant in Chautauque county, forming layers of several inches thick 
and many yards in extent. Localities, Chautauque creek ; Twenty-mile creek. 
5. Delthyris acuminata, n. s. — Transversely elongated ; hinge line much extended into 
long acuminate points ; mesial fold simple, well defined ; surface marked by sixteen simple 
ribs, which are crossed by abruptly undulating elevated lamellae, usually much better seen in 
the external casts of the shell. 
5 and 5 a. Internal casts of the upper and lower valves, 
5 h. Enlarged portion of a cast of the external surface. 
Localities —Ithaca ; Chemung ; Cayuta creek. 
124. 
1. Atrypa dumosa. 2. Atrypa hystrix. 3. Atrypa trtbulis. 4. Atrypa? tenuilineato. 
