AMERICAN PALEOZOIC CEPHALOPODS 
245 
to develop. In other words, Beloitoceras may be regarded as the 
stock from which Maelonoceras developed. 
Cyrtoceras mrrollense Worthen, Oncoceras carvieri Clarke, 
Cyrtoceras fragile Billings, C. houghtoni Clarke, C. huronense 
Billings, C. isodorus Billings, C. norwoodi Clarke, and C. scofieldi 
Clarke are congeneric; probably also an equal number of other 
described species of which the living chamber is not well known. 
Cyrtoceras dunleithense Miller and Gurley, and C. cordatum 
Parks are characterized by the ridge-like protrusion of the siph- 
onated Side of the conch, and for these the generic term Dun- 
leithoceras is proposed. 
40. BELOITOCERAS PANDION HALL 
PLATE XXXVI, FIGS. 5 A, B; PLATE XLI, FIGS. 4 A, B, C 
Oncoceras pandion Hall; Rep. Sup. Geol. Surv. Wisconsin, 1861, 
p. 45, ibid, 1862, p. 41, fig. 3 
Oncoceras pandion Whitfield; Mem. Amer. Mus. Nat. Hist., vol. 1, 
pt. 2, 1895, p. 69, pi. 9, figs. 21, 22 
• Type. — Conch strongly curved lengthwise, especially along its 
ventral side, where the radius of convex curvature is only 30 mm. 
Along the dorsal side the radius of concave curvature is 40 mm. 
The specimen enlarges from a dorso-ventral diameter of 19 mm. 
at its base to 25 mm. at the base of the living chamber. It 
diminishes to 22.5 mm. along a line drawn from 10 mm. above 
the base of the dorsal side of the living chamber to 14 mm. above 
the base of this chamber on the ventral side. Then this diameter 
diminishes rather abruptly, to 21 mm. within a distance of 3 mm., 
and to 20 mm. within an additional distance of 4 mm., above 
which the margin of the aperture is assumed to be. The cor- 
responding lateral diameters are 16 mm. at the base of the speci- 
men, 23 mm. at the base of the living chamber, 20 mm. where the 
abrupt contraction of the upper part of the living chamber be- 
gins, 16.5 mm. at a point 3 mm. farther up, and slightly less at 
the aperture. The sudden constriction of the cast of the interior 
of the living chamber near the aperture indicates the presence of 
a corresponding thickening of the interior of the wall of this 
chamber just beneath the aperture. 
There is no trace of a gibbosity along the dorsal outline of the 
conch at the base of the living chamber, though the amount of 
concave curvature here is distinctly less. The cross-section of 
the conch tends to be slightly more narrowly convex on the ven- 
