CEPHALOPODA. 805 
Oyrtoceras camurum.] 
the slight deepening of the air-chambers on the ventral surface and also the recurved 
surface striae which have a direction nearly the reverse of that of the septa. 
Formation and locality.—In the Trenton limestone at Cannon Falls, Minneapolis and near Foun- 
tain, Minnesota, and Beloit, Wisconsin; in the Galena shales at Wykoff, Minnesota, 
Museum Register, Nos. 6554, 7926. 
CyrtoceraAs camuruMm Hall, 1847. 
PLATE LX, FIGS. 5, 6. 
Cyrtoceras camurum HALL, 1847. Paleontology of New York, vol. i, p. 196, pl. xin, fig. 6. 
Cyrtoceras camurum WHITFIELD, 1882. Geology of Wisconsin, vol. iv, p. 231, pl. vil, figs. 7, 8, 9. 
The very gradual expansion, slight arcuation and extreme lateral compression 
of this species afford a ready distinction from associated forms. The original 
specimen, from Middleville, N. Y., is not very favorably preserved, but that figured 
by Whitfield serves to establish the characters of the species and with the latter I 
find a close agreement in the case of a single specimen in the collections in hand. 
This retains the entire body-chamber and sixteen air-chambers, and also shows the 
bead-lke divisions of the submarginal sipho. 
Formation and locality—In the upper buff beds of the Trenton limestone, Samp’s quarry, Beloit, 
Wisconsin, 
CyrTOCERAS HALLIANUM D’Orbigny, 1850. 
PLATE LX, FIGS. 11, 12, 
Cyrtoceras lamellosum HALL, 1847. Paleontology of N. Y., vol. i, p. 938, pl. Xut, figs. 2a-c. 
Cyrtoceras hallianum D’ORBIGNY, 1850. Prod. de paléontol. stratigraph., vol. i, p. 1. 
Cyrtoceras billingst SALTER, 1859. Figures and Descr. Canad. Org. Rem, Decade 1, p. 33, pl. vu, 
fig. 5 (non 6). 
The original of this species was a small, badly crushed specimen distinguished 
by its surface ornamentation, consisting of “undulating squamose lamelle 
which are abruptly bent backward on the dorsal line.” There are two specimens 
before me in which this peculiar ornament is retained; one a mere fragment of the 
shell with these surface markings very sharply defined, the other a considerable 
portion of a large and more complete example in which the surface is less clearly 
preserved. The latter shows an arcuate and broad shell with ovate cross-section, 
the dorso-ventral diameter diminishing, in a length along the ventral periphery of 
60 mm. (and dorsal of 37 mm.), from 25 mm. to 16 mm. 
Septa rather closely crowded, eight or ten on the dorsal surface of 37 mm., 
inclining somewhat to the venter. Sutures with low, scarcely perceptible lateral 
lobes. Sipho ventral, submarginal. 
