304 PALEONTOLOGY OF NEW YORK 



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. calamen, but somewhat finer, and the frequency and prominence 

 of the annulations are very different. The annulations are sharper and more 

 abrupt than in O. Theslor, and it has not the continuous, longitudinal, elevated 

 stria? 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. Bebryx, 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. 



ORTHOCERA.TA. 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- 



