AMERICAN PALEOZOIC CEPHALOPODS 
239 
mond, Indiana. The large specimen forming the basis of most of 
the description here presented was obtained on Dodge's Fork, 
near Oxford, Ohio, at the base of the Whitewater member of 
the Richmond formation. Numerous specimens from the same 
horizon, on Little Four Mile creek, also near Oxford, furnished 
additional material, including sections of the siphuncle. How- 
ever, most of the details of the structure of the siphuncle here 
presented were obtained from a specimen collected by Prof. J. E. 
Carman on Flat Fork, three and a half miles northeast of Ore- 
gonia, Ohio, at the base of the Whitewater. The specimens from 
the vicinity of Oxford belong to Miami University and were col- 
lected by Professors W. H. Shideler and S. R. Williams. 
A closely similar, if not identical, species occurs at the base of 
the Rhynchotrema dentata bed in the Upper Whitewater, on 
Beasley Run, north of Camden, Ohio. 
Specimens resembling Charactoceras haeri occur in the Fern- 
vale member of the Richmond at Wilmington, Illinois, and Cape 
Girardeau, Missouri. 
34. ONCOCERAS HALL 
Genotype: Oncoceras constrictum Hall. Pal. New York, vol. 1, 1847, 
p. 197, pi. 41, figs. 6 a-f, 7 a-d 
Conch curved lengthwise; the lengthwise curvature of the 
ventral side is convex, and the general curvature of the dorsal 
side is concave, but along the upper part of the phragmacone 
and the lower part of the living chamber the vertical outline of 
the dorsal side changes to distinctly, though moderately, convex. 
The gibbosity of the dorsal side of the conch usually extends also 
laterally sufficiently to be noticeable when the conch is exam- 
ined from the ventral side. The conch is slightly compressed 
laterally. The living chamber narrows toward the aperture, 
which is broadly oval in outline, the angularity being on the 
ventral side. The hyponomic sinus is shallow. The siphuncle 
is close to the ventral wall of the conch, and its segments are nar- 
rowly fusiform. 
Oncoceras abruptum Hall, Gomphoceras cincinnatiense Miller, 
Oncoceras douglassi Clarke, Oncoceras pristinum Ruedemann, 
and Orthoceratites trentonense Emmons are congeneric. The 
last named species from the Trenton of New York apparently is 
identical with Oncoceras constrictum, Gomphoceras faberi 
