304 
PALAEONTOLOGY OF NEW Y OR Li 
The specimen figured and described has a length of forty-three mm., and 
shows thirty-four annulations. 
This species is distinguished from 0. Idmon by the characters of its surface 
and the concave, interannular furrows. The surface-markings are very similar 
to those of 0. ccdamen , but somewhat finer, and the frequency and prominence 
of the annulations are very different. The annulations are sharper and more 
abrupt than in 0. Thestor, and it has not the continuous, longitudinal, elevated 
strife of that species. 
Formation and locality. In the coarse shales of the Hamilton group at 
Cazenovia, N. Y. 
Orthoceras, sp. indet. 
PLATE LXXXIII, FIG. 13. 
A large fragment, of obscure specific characters, has been observed among 
collections made from the calcareous beds of the Hamilton group at West 
Williams, Ontario, Canada. In its form and proportions it bears considerable 
resemblance to 0. JBebryx, but is too imperfect for satisfactory reference. The 
specimen is a weathered cast of the interior of the chamber of habitation and 
the last air-chamber. The last septum and portions of the walls of the grand 
chamber are covered with numerous individuals of a species of Spirorbis, which 
do not appear to have penetrated to the preceding septum. 
ORTHOCERATA OF THE PORTAGE GROUP. 
The Portage group, as recognized in Central and Western New York, consists 
of a series of finely laminated, black and olive shales, and argillaceous sand¬ 
stones, with a few interrupted intercalations of semi-calcareous bands. This 
series of beds directly succeeds the Genesee slate, which may be regarded as 
the termination of the Hamilton group, or as beds of passage connecting it with 
the Portage. This group has yielded few forms of Orthoceratites. In those 
portions where the shaly deposit has assumed a semi-calcareous character, there 
has been an increase of animal life, and the fauna is characterized by a large 
proportion of Goniatites and an increased number of Orthoceratites, indicating 
more favorable conditions for their development. Owing to the limited collec- 
