110 
GEOLOGY OF THE FOURTH DISTRICT. 
1 and 2. Euomplialus hemisphericus, n. s. — Convex, hemispherical; volutions about four, 
crossed by striae and elevated lines of growth. 
This fossil usually occurs as a cast in the Niagara limestone, and consequently the charac¬ 
ters of the shell are not perfectly known. 
Localities —Rochester and Lockport, in limestone. 
3. Cornulites arcuatus (Conrad, Jour. Acad. Nat. Sci. Vol. 8, p. 276, pi. 17, f. 8).— 
Conical, rapidly attenuated ; composed of a series of cup-form disks, placed above and in¬ 
serted within each other at the margins. 
The annulations are more rounded than in C. serpularius of the Wenlock limestone (See 
Silurian Researches, p. 627, pi. 26, f. 5). It is easily distinguished from any other fossil in 
the group, or even in the system. It occurs in single specimens at Rochester in the lime¬ 
stone, and at Lockport in groups, in cavities which are partially filled with spar. The fossil is 
usually nearly destroyed, its form being left invested with crystals, and sometimes a small 
central tube or siphuncle? is all that remains. 
1. Orthoceras annulatum? — Very gradually tapering ; ornamented with transverse rings, 
and numerous undulating lines ; siphuncle central. Diameter 11 to 2 inches. 
In many respects, this resembles the figure of O. annulatum (Silurian Researches, pi. 9, 
f. 5); and more nearly the figure of the same in Mineral Concliology, t. 133; but it is de¬ 
stitute of longitudinal furrows or arched laminae. Since, however, that species is variable in 
its characters, it may be the same. The specimen figured is a flattened fragment from the 
