94 
PALEONTOLOGY OF NEW-YORK. 
CEPHALOPODA OF THE CLINTON GROUP. 
The fossils of this family are so rare as scarcely to attract attention, though there are a 
few interesting forms which are almost entirely restricted to the lower part of the group. The 
most remarkable genus is the Ormoceras, of which a single species occurs in great numbers in 
the Black-river limestone; while it is extremely rare in the Trenton limestone, and appears 
again in the Hudson-river group, and there only as a single species. Until within a short period, 
this genus has been unknown above the Lower Silurian period in our country ; but, from 
fragments occurring in the strata under consideration, and in a higher position, it is probable 
that this genus extends throughout the silurian strata. 
489. 3. ONCOCERAS SUBRECTUM (». sp.). 
Pl. XXVIII. Fig. 11 a, b. 
Fragment subfusiform or conical, abruptly enlarging from the smaller extremity, and 
contracted towards the aperture, slightly curved ; surface marked by fine, slightly uneven, 
transverse striae. 
This specimen, at first view, appears like Gomphoceras ; but it still retains a slight curve, 
increasing towards the smaller extremity, but which, from the specimen having been com¬ 
pressed, is not so obvious in the figure. The transverse section is oval, but owing to pres¬ 
sure towards the aperture that portion is quite flattened, so that the contracted aperture of 
Oncoceras is not characteristic in the specimen. The surface is plainly striated, except on the 
inner side of the curve for a short distance there is a suture, producing an abrupt arching in 
the striae. 
Fig. 11 a. Lateral view of the fragment, 
Fig. 11 b. A portion of the surface enlarged, showing a suture on one side. 
Position and locality. In the lower cherty layers of the group at Lockport. 
490. 4. ORMOCERAS VERTEBRATUM. 
Pl. XXIX. Fig. 1 a- g. 
Shell elongated, gradually tapering, section circular ; siphuncle nearly central ; surface 
unknown ; septa four to five in the space of an inch ; edges of the septa slightly projecting 
in the cast, and the spaces between them contracted or concave ; siphuncle presenting the 
usual appearance of Ormoceras, the longitudinal diameter of the expanded portions being about 
one half as great as the transverse diameter. 
This species, which occurs in casts or fragments, bears considerable resemblance to Ormo¬ 
ceras tenuijilum of the Black-river limestone ; but the septa are more convex and somewhat 
