AMERICAN PALEOZOIC CEPHALOPODS 
247 
consin, figured by Clarke,^® the lengthwise curvature of the ven- 
tral side of the conch is similar, but the concave curvature of the 
dorsal side is greater, especially along the lower part of the 
living chamber ; the conch is more compressed laterally, and the 
sutures do not rise as strongly on the ventral side of the phrag- 
macone. 
Oncocevas carvieri Clarke®^ appears to be closely related to the 
Platteville specimen figured by Whitfield under Oncoceras 
pandion. It is characterized chiefly by its lateral compression, 
and the fact that the living chamber is not so strongly con- 
tracted toward the aperture. 
41. BELOITOCERAS PLEBEIUM HALL 
PLATE XXXVI, FIGS. 4A, B, 3 A, B; PLATE XLI, FIGS. 5A, B 
Oncoceras plebeium Hall; Rep. Superintendent Geol. Surv. Wisconsin, 
1861, p. 44 
Oncoceras plebeium Whitfield, Mem. Amer. Mus. Nat. Hist., vol. 1, pt. 2, 
1895, p. 68, pi. IX, figs. 16-19 
The original description indicates that several specimens were 
at hand at the time of description of this species. Of these Whit- 
field figured three. The largest is selected as the type because it 
bears the small lozenge-shaped yellow label, and retains a rem- 
nant of the thin paper label which Hall used for indicating his 
types among the species described in 1861. Moreover, this speci- 
men is the first one of the three figured by Whitfield.^® 
Selected type . — Specimen (Plate XXXVI, Figs. 4A, B; Plate 
XLI, Figs. 5 A, B) consisting of the living chamber with 7 cam- 
erae still attached. Conch rather strongly curved lengthwise in 
a dorso-ventral plane ; the radius of convex curvature of the ven- 
tral side, along the upper part of the phragmacone and along the 
living chamber, is 45 mm. ; the radius of concave curvature of 
the dorsal side, along the upper part of the phragmacone, is 
30 mm. ; a very faint convexity extends from the base of the 
second camera below the living chamber upward along the 
greater part of the living chamber, but within 3 or 4 mm. from 
the aperture the dorsal outline is slightly concave again. The 
faint convexity along the lower part of the dorsal side of the liv- 
Clarke, John M., The Lower Silurian Cephalopoda of Minnesota; Minn. 
Geol. Survey, Final Rept., vol. 3, pt. 2, p. 799, pi. 58, figs. 4-6a, 1897. 
Idem. p. 799, pi. 58, figs. 7-9. 
Whitfield, R. P., Republication of descriptions of fossils from the Hall 
collection; Mem. Am. Mus. Nat. Hist., vol., 1, pi. 9, figs. 15, 16, 1895. 
