308 
PALAEONTOLOGY OF NEW YORK. 
approaching this in the position of the siphuncle, have much more distant 
septa, as 0. exile and 0. Telamon. 
The specimens from the soft shales are usually very much flattened from 
compression. Those in the calcareous layers preserve their normal propor¬ 
tions, with fragments of the test, and are fllled and replaced by iron pyrites, 
which has obscured several features of the septa and siphuncle. 
Formation and localities. From the shales of the Portage group, in the vicinity 
of Ithaca, and in the calcareous layers of the group at Mount Morris, N. Y. 
ORTHOCERATA OF THE CHEMUNG GROUP. 
The lower shales and calcareous beds of the group furnish very few distinc¬ 
tive forms, and these have but a limited horizontal distribution. The central 
portion of the group has afforded few specimens, and these are usually in such 
unsatisfactory condition that they cannot be distinctly characterized. The 
upper members, generally consisting of arenaceous strata, give evidences of a 
more extensive development and distribution of these forms, but the beds have 
not yet been critically examined. 
The Orthoceratites of the Schoharie grit and Upper Helderberg limestones 
may be characterized by the predominance of large and robust species. The 
Hamilton group is distinguished by the excess of slender and annulated forms, 
The Chemung group, so far as observed, in its remarkable annulated form, 
and several short, ventricose, rapidly enlarging species, presents transitional 
features from the robust to the slender forms, and between the smooth and 
annulated species. A more extended account of the species occurring in this 
group will be presented in a future supplementary notice of the genus. 
Orthoceras cochleatum, n. sp. 
TLATE CXI1I, FIG. 19. 
Shell straight, regularly and rapidly enlarging to the chamber of habitation. 
Transverse section circular. Apical angle 15°. Initial extremity acute. 
Chamber of habitation slightly gibbous, having a length equal to more 
than once and a half the diameter of the tube at the last septum. The tube 
