1JTICA SLATE ANII HUDSON-RIVER GROUP. 



309 



CEPHALOPODA OF THE UTICA SLATE AND HUDSON-RIVER GROUP. 

 Plates LXXXV., LXXXVI. & LXXXVII. 



Tlic rocks of this group funiisli few species of Cephalopoda in addition to those already- 

 described. The Orthocerata 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 ; Imt these arc often obscure, and their 

 determination unsatisfactory. 



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

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

 here described or not. 



249. 1. TROCHOLITES AMMONIUS. 



Pl. LXXXIV. Figs. 2 a, b, c. 



Reference pag. 192, pl. 40, figs. A a -k, of this volume. 



TrochoKtes rugosus. Conrad in M.S. State Collection. 



Trocholites, Utica trocholite. V.\ndxem, Geol. Report, 1S42, pag. .')7, fig, 3. 



This fossil is clearly identical with T. ainmonius of tlie 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 tliat it continued to 

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

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



Fig. 2 a. A small specimen, 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 

 heckii. 



