CEPHALOPODA. 801 
Oncoceras carveri.] 
This species is distinguished by its subacute venter, broad but not ventricose 
dorsal surface and the very slight decrease in the diameter of the body-chamber 
from its base to the constriction. 
Formation and locality —The species appears to be quite common in the lower blue beds of the 
Trenton limestone at Janesville, Wisconsin. It also occurs in the Trenton at Preston and Minneapolis, 
Minnesota. 
Museum Register, No. 8300. 
ONCOCERAS CARVERI, sp. nov. 
PLATE LVIII, FIGS. 7—9. 
An entire body-chamber, with three air-chambers attached, is characterized by 
its broad sides, narrow dorsum and compressed, subangular venter. The cross- 
section of the shell is, thus, elongate-ovate, its major and minor diameters being as 
3 to 2. Above the third septum (counting from the aperture) the shell expands 
somewhat to within the base of the body-chamber and is, thence, gently contracted 
to the aperture. The latter is more narrowly ovate than the rest of the shell, its 
lateral margins convex, making a narrow emargination on the venter. The suture 
is transverse on the sides and dorsum, without curvature, but is curved forward 
over the venter to such a degree that the depth of the air-chambers at the ventral 
surface is about twice that on the dorsal surface. 
The sipho is ventral and is situated within the margin of the septa. 
The shell is but slightly arcuate, being suberect except in the vicinity of the 
aperture where it is curved inward making the aperture somewhat oblique. Sur- 
face covered with fine concentric strie which are strongly recurved over the 
venter, concentric to the outline of the aperture. The length of the body-chamber 
in the specimen is 20 mm.; the entire length of the body-chamber with three air- 
chambers, 26 mm.; the major diameter of the third septum, 21 mm., the minor 
diameter, 14 mm. 
Formation and locality.—In the Trenton limestone at Minneapolis, Minnesota. A fragment of a 
larger shell has also been observed in the upper buff beds at Rockton, Illinois. 
Museum Register, No. 2193. 
ONcOCERAS DOUGLASSI, Sp. 200. 
PLATE LXI, FIGS. 13-15. 
Shell arcuate over the earlier portion, suberect for the greater part of its 
length. From the eighth air-chamber (counting from the aperture) upward, the 
shell expands rapidly to the last septum, thence contracts more rapidly, forming a 
broad and rather deep constriction just within the aperture. The expansion is 
