492 



NEW YORK STATE MUSEUM 



shaped disks concentric to the siphuncle. Septa very flat, their depth 

 not quite equal to that of the cameras. Living chamber observed 

 only in its posterior portion. Aperture not seen, the hyponomic 

 sinus either extremely shallow or situated on the inner side (endo- 

 gastric shell), for the growth liner are straight transverse on the 

 outer side. 



Siphuncle centren, highly nummuloidal in all parts of the 

 phragmocone, about 2 mm in the interseptal expansion, rilled 

 by organic deposits arranged in rosettes around the septal necks and 

 leaving open an endosiphotube and radiating tubuli. The surface is 

 smooth. 



Position and localities. This form has been found most com- 

 monly in the exposure of the dove-colored limestone near the cross- 

 ing of the Chazy turnpike and Little Monty bay road, 2 miles 

 south of Chazy. Fragmentary sections, which are referable to this 

 species, have also been obtained by Prof, van Ingen in the Saranac 

 river at Plattsburg. 



Observations. This cyrtoceracone is readily distinguished 

 from other forms of the Chazy and Trenton periods by its rapid 

 expansion, the centren position and nummuloidal character of its 

 siphuncle ; from the preceding species with which it is associated 

 and with whose young it might be confounded, it differs mainly in 

 its smaller curvature and relatively smaller siphuncle. 



Genus gonioceras Hall 



In the first volume of the Palaeontology of New York 

 [1847, P- 54] Kail erected the genus Gonioceras for a cephalopod 

 from the Black river beds at Watertown, which offered a very 

 peculiar aspect. Later on the same author 1 described another species 

 from the Trenton of Wisconsin and these are the only two species 

 of the genus which have thus far become known. A third species, 

 which had been announced by Whiteaves from the Trenton of Mani- 

 toba, has later been referred by Clarke to Triptoceras. The last 

 named author, who has also recorded the presence of the two species 

 of Gonioceras in the Trenton of Wisconsin, Minnesota and Illinois, 

 gives the following diagnosis of the genus [1897. p. 794]. 



Broad, flat, straight shells, extremely compressed dorsoventrally, 

 and with extended lateral flanges into which the septa are continued. 

 The shells are subcqually biconvex with regular concave dorsal and 



1 Report of Progress, Wis. 1861. 



2 Roy. Soc. Can. Proc. 1891. v. 9, section 4, p. 86. 



