GUELPH FAUNA IN THE STATE OF NEW YORK 93" 



Billings, by the fact that the latter is annulated and from G. bannisteri 

 Winchell & Marcy, 1 from the western Niagaran, for the same reason. 



POTEBIOCEBAS McCoy. 1 844 



Poterioceras sauridens sp. nov. 



Plate 14, fig. 1-19 



The most common and one of the most characteristic cephalopods of 

 the lower bed at Shelby is a small breviconic cyrtoceracone, different in 

 important characters from all other forms reported from the Guelph or 

 so called Niagaran horizons. A single specimen somewhat crushed dorso- 

 ventrally was also obtained at Rochester. 



Diagnosis. Shell small, fusiform, somewhat abruptly tapering and 

 relatively but little curved ; in a specimen with a length of 48 mm the outer 

 arc has a hight of 19 mm ; the inner of 4 mm, measured from a chord con- 

 necting the extremities. The shell is slightly asymmetric, and seen from 

 the ventral side, the apex is turned a little to the right. It is somewhat 

 compressed dorsoventrally, in its mature parts the dorsoventral diameter 

 being one tenth shorter than the lateral ; the dorsum is almost flat or but 

 slightly rounded, while the ventral side is well rounded, its section in most 

 specimens being part of a circle. The ventrolateral slopes are evenly 

 rounded, while the dorsolateral are quite abrupt. In the apertural part the 

 section is entirely circular, the flattening of the dorsal side not appearing 

 till about the neanic stage of the shell. The living chamber is remarkably 

 short ; its length rarely attains that of the diameter of the last septum ; this 

 chamber is widest at about one third of its length, whence it contracts on the 

 ventral and lateral sides, toward the aperture to such a degree that the 

 dorsoventral diameter of the aperture becomes slightly the smaller. The 

 outline of the aperture is simple, with a shallow hyponomic sinus and a 

 broad, low dorsal saddle. The shell around the aperture is thickened, so 

 that on the very frequent casts of the living chamber, there appears a ring- 

 like depression just within the margin. 



■According to Hall, N. Y. State Mus. 20th An. Rep't, supplementary note, p. 393, this 

 is a Trochoceras. 



