tJTICA SLATE AND HUDSON-KIVER GROUP. 309 



CEPHALOPODA OF THE UTICA SLATE AND HUDSON-RIVER GROUP. 



Plates LXXXV., LXXXVI. & LXXXVII. 



The rocks of this group furnish few species of Cephalopoda in addition to those already 

 described. The Orthoceilata are usually found in fragments, entirely denuded of the 

 shell, and so much compressed as to render it difficult to identify them. Several species, 

 apparently identical with those previously described, are found ranging through the group. 

 Among these, the young shells of Endoceras proteiforme are the most abundant, particularly 

 in the Utica slate. Two or three previously unknown forms appear in the higher part of 

 the group, where some of the strata are calcareous ; but these are often obscure, and their 

 determination unsatisfactory. 



In the western extension of the group, in Ohio and Indiana, I have observed several 

 species of Orthoceras, but have not yet determined whether they are identical with those 

 here described or not. 



249. 1. TROCHOLITES AMMONIUS. 



Pi> LXXXIV. Figs. 2 a, b, c. 



Reference pag. 193, pi. 40, figi. 4 a- Ic, of this volume. 

 Trocholitea rugoius. Conbad in MS. State Collection. 

 Trocholitei, Utica trocholite. Vanuxem, Geol. Report, 1842, pag. 57, fig. 3. 



This fossil is clearly identical with T. ammonius of the Trenton limestone, the difference 

 observable in some specimens being due to the character of the enclosing shale, or to the 

 partial exfoliation of the shell. Its appearance in this position shows that it continued to 

 exist in considerable numbers after the cessation of the calcareous deposits below ; and, on 

 this account, we may look for its occurrence in the shales of the Hudson-river group. 



Fig. 2 a. A small specjmen, partially preserving the shell in some parts, and showing the septa in 



others. 

 Fig. 2 b. An enlarged portion of the surface, which is partially exfoliated, and slightly different from 



similar magnified parts of those in the Trenton limestone, where the shell is well preserved. 

 Fig. 2 c. Mould of a large specimen, in the black slate. 



Position and locality. This species occurs in the Utica slate on East-Canada creek, at 

 Canajoharie ; Cold-spring, on the Erie canal ; and in other places, associated with Calymene 

 beckii. 



