9 2 



NEW YORK STATE MUSEUM 



described 1 as having the dorsal and ventral sides equally rounded, and it 

 also possesses deeper camerae. 



This species, C. curvicameratum, is considered a typical repre- 

 sentative of the genus Cyrtorhizoceras Hyatt 2 on account of its uncontracted 

 living chamber, open aperture and the character of its dorsal and hyponomic 

 sinuses, its laterally compressed form, the well developed ventral and dorsal 

 saddles of the sutures and the small siphuncle. The genus is described as 

 beginning in the Lower Siluric, where the generic type, Cyrtorhizo- 

 ceras minnesotense Clarke (sp.), a small form of the western Tren- 

 ton, occurs, and as extending into the Upper Siluric. It appears that this 

 genus, a very primitive group of cyrtoceracones, is still well represented in 

 the Niagaran, for several of the western species of Cyrtoceras evidently 



pertain to it. 



gykoceras de Koninck. 1844 



Gyroceras farcimen sp. nov. 



Plate 18, fig. 1-4 



Diagnosis. Conch robust, strongly curved, very slowly expanding, 

 number of volutions unknown ; transverse section circular, the dorsal and 

 ventral sides not appreciably different in curvature, no impressed zone 

 observable ; camerae moderately deep, septa 8 mm distant, where the diam- 

 eter of the shell is 28 mm ; sutures transverse, nearly straight, a small saddle 

 at the outer side of the arch ; siphuncle submarginal, at the outer side its 

 character not known ; living chamber very long, extending for one half a 

 volution or more, continuing with the curvature of the septate portion ; 

 aperture not known ; surface smooth. 



Locality. Lower Shelby dolomite. 



Observations. There are only three cephalopods with gyroceran volu- 

 tions known from the Niagaran; G. farcimen may be readily distin- 

 guished from G. abruptus Hall, of the Indiana Niagaran, by its very 

 gradual expansion and the position of its siphuncle, from G. americanum 



1 Report of Pi-ogress of Geological Survey of Wisconsin for i860, p. 43. 

 »Zittel-Eastman. Textbook of Paleontology. 1900. p. 529. 



