268 
GEOLOGY OF THE FOURTH DISTRICT. 
2. Orthis impressa, n. s. — Circular ; hinge line short; upper valve nearly flat, suddenly 
depressed in front (as if the finger had been applied when the shell was flexible); surface 
covered with fine equal strias, which are more strongly marked upon a narrow border on the 
margin; cast of the muscular impression at the beak small, bilobate by a narrow sinus. 
The form is perfectly represented in the figure, which is a cast. It is often associated with 
the next species in the soft and green shales about Elmira and elsewhere. 
3 and 4. Orthis interlineata (Sowerby in Geol. Trans., 2d series, vol. 5, pi. 54, fig. 14. 
Phillips, Palceozoic Fossils, p. 63, pi. 26, f. 106.) — Transversely elliptical, depressed; 
hinge line much less than the width of the shell; upper valve flat, with a ridge along the 
centre ; lower valve moderately convex, with a shallow depression from beak to base ; surface 
radiated by numerous unequal or divaricating striae. 
Fig. 3 is a cast of the upper valve, in which the inequality of the striae are less perceptible. 
Fig. 4, lower valve, showing near the beak the spaces from which the subrostral plates 
have been removed. 
The figures of Sowerby correspond better with our fossils than those of Mr. Phillips. The 
casts, however, fig. 3 above, and 106 a of the latter, very closely resemble each other, and 
there can be no doubt of the identity of the fossils. 
Localities —Cayuta creek ; Chemung; Elmira. 
5. Orthis unguiculus. (Atrypa unguiculus, Sowerby in Geol. Trans., 2d series, vol. 5, 
pi. 54, fig. 8. Spirifera unguiculus, Phillips, Pal. Fossils, pi. 26, f. 119.)—Hemispherical, 
varying in the proportions of length and breadth; beak large, inflated and incurved; lower 
valve very convex, with a central impressed line extending a part or the whole distance from 
beak to base; upper valve flat, or slightly convex on each side of a depressed line in the 
centre. 
This fossil usually appears as casts, frequently abundant, and covering surfaces many feet 
in extent. 
5 a. Cast from Bald hill, near Ithaca. 
6. Lower valve ; broad variety. Dexterville, Chautauque county. 
c. Upper valve. Painted-post, Steuben county. 
d. Fragment of brownish sandstone, covered with casts of the shell. Jasper, Steuben 
county. 
This fossil differs from the 0. umbonata of the Hamilton group, which it considerably 
resembles. 
