308 I'ALJEONTOLOGY OF NEW YORK. 



approaching this in the position of the siphuncle, have much more distant 

 septa, as 0. exile and O. 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 filled 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. 



Okthoceras cochleatum, n. sp. 



PLATE C.XI1I, HG. 19. 



Smell 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 



