GUELPH FAUNA IN THE STATE OF NEW YORK 89 



referred by Whiteaves r with some doubt to this species. This contraction 



may be here a gerontic character, as it has been claimed by Pompeckj and 



Hyatt that numerous cephalopods constrict their apertures in gerontic 



stages. 



Cyrtoceras cf. brevicorne Hall 



Plate 13, fig. 11, 12 



See Cyrtoceras brevicorne Hall, N. Y. State Cab. Nat. Hist. 20th An. Rep't. 

 1867. p. 356, pi. 18, fig. 8, 9 



A small, rapidly expanding cyrtoceracone from the Rochester collec- 

 tion, though quite incomplete, seems to agree with Cyrtoceras brevi- 

 corne Hall in the rapid expansion of the shell. In a length of 16 mm 

 it expands from 5 to 12 mm in diameter. The section is oval, broadly 

 rounded on the ventral and more acutely on the dorsal side. The inner 

 curvature is slight. Septa shallow, curving strongly downward on the 

 venter. The siphuncle is small and situated close to the ventral margin. 

 The chamber of habitation is not preserved in the specimen. The surface 

 is smooth or covered with fine concentric growth lines, which show a 

 broad and deep posterior curve on the venter. 



The original specimens of this species were from the dolomite at 

 Racine Wis. The form has not yet been observed in either the Canadian 

 Guelph or the Niagara beds of New York, but is reported from several 

 outcrops of the Racine beds in Wisconsin. 2 



In the lower Guelph bed at Shelby has been found a short conch, which 

 in its extremely rapid expansion and curvature agrees with Hall's figured 

 specimen of Cyrtoceras brevicorne, but fails to show the difference 

 in convexity of the dorsal and ventral sides. Its section is, on the contrary, 

 perfectly circular. 



1 Loc. cit. pi. 14, fig. 9. 

 2 Geol. of Wisconsin, 2 : 376 



