45 



Geological Formation and Locality, In the Buff limestone 

 of the Trenton limestone group, at Beloit. 



Collectors. Prof. Nason, E. Eolart T. J. Hale. 



ONCOCERAS pandion, (n. s.) 



Description Shell robust, strongly curved, very rapidly 

 expanding to near the outer chamber, which gently decrease? 

 in size for nearly two-thirds of its length, and then becomes 

 suddenly constricted to nearly half its former dimensions: 

 broadly ovate or sub-circular, the diameter in the dorso-ventral 

 direction. Septa moderately distant, strongly curved forwards 

 on the dorsal side, the greatest concavity on the ventral side 

 of the centre. Siphuncle large, dorsal. 



Surface unknown. 



This species most nearly resembles in form the 0. comtrictum 

 of any species yet found in Wisconsin. The differences con- 

 sisting in the greater proportional transverse diameter, the ab- 

 sence of a prominent or ventricose space on the vental side at 

 the point of greatest diameter, the greater concavity of the 

 septa, and the more sudden contraction of the aperture. 



Geological Formation and Locality, In "Buff limestone" of 

 the Trenton limestone group, at Beioit, Wisconsin. 



ONCOCERAS lvcum, (n. s.) 



Shell somewhat gently curving, gradually expanding from 

 the middle to the outer chamber, which is marked by a broad, 

 deep constriction just posterior to the aperture, the margin of 

 which is expanded or sub-reflex. Transverse section very 

 broadly ovate, the diameters as nine and ten, the longest being 

 in the dorso-ventral direction ; very obtusely snb-angular on 

 the back. Septa slightly concave, about a line apart, one or 

 two of the outer ones a little more approximate. Siphuncle 

 of medium size, expanded within the chambers, placed at 

 about its own diameter within the dorsal margin. Length of 

 fragments one to two inches. Entire length of larger speci- 

 mens, three or four inches. 



This species bears some resemblance to 0. pandion iii the 

 form of the transverse section, and the constriction near the 

 aperture, nut differs in the curvature of the shell, and in hav- 

 ing less concave septa and position of the siphuncle. 



Geological Formation and Locality. In the "Buff limestone" 

 of the Trenton limestone group. 



