808 THE PALEONTOLOGY OF MINNESOTA. 
| Cyrtoceras minneapolis. 
the ventral side. This implies that the depth of each chamber on the venter is 
very much greater than on the dorsum. Hach suture makes a low, broad and very 
obscure saddle on the dorsum, scarcely perceptible lateral lobes, thence sloping 
forward and making a strong ventral saddle. 
Sipho ventral and submarginal. Body-chamber large and deep on the dorsum, 
equalling ten air-chambers in length, and on the venter six. Surface smooth. 
Dimensions. The specimen upon which this species is based retains the body- 
chamber nearly intact, and thirteen air-chambers. It has a length of 36 mm. on 
the outer curve, 11 of which belong to the body-chamber; on the inner curve it 
measures 28 mm., of which 11 belong tothe body-chamber. Its transverse diameter 
near the aperture is 14 mm.; at the last septum 13 mm., and at the thirteenth 
septum 7mm. Its dorso-ventral diameter near the aperture is 12 mm., at the last 
septum 11 mm., and at the thirteenth septum 6 mm. 
This species is well characterized by the peculiar transverse form the shell. 
Formation and locality.—The type specimen is from the Trenton limestone, and is believed to have 
been obtained from Madison, Wisconsin. Collection of W. H. Scofield. 
CYRTOCERAS MINNEAPOLIS, Sp. 00, 
PLATE LIX, FIGS. 1—8. 
Shell arcuate, rapidly expanding to the aperture. Body-chamber without con- 
striction ; apical curvature not known. Surface laterally compressed ; sides broad ; 
dorsum narrow, venter still narrower and more arcuate. Transverse section 
subelliptical, the major and minor diameters being as 11 to 9 at the next to the 
last septum, and as 16 to 11 at the aperture. The lateral margins of the aperture 
are convex, the dorsal and ventral margins broadly and narrowly concave or 
re-entrant, respectively. The septa are regularly and evenly, though not deeply 
concave, the deepest concavity being at about the center. The sutures are 
transverse and simple, without lobes or saddles save fora slight upward inclination 
on the venter, which gives to the air-chambers.a greater depth on the ventral than 
on the dorsal side. Sipho ventral, submarginal, expanded in each air-chamber. 
Surface covered with closely crowded concentric lines, conforming in curvature 
to the aperture. On the internal cast are traces of longitudinal ridges over the 
body-chamber. 
A small and typical example has the aperture 16 mm. in major, and 11 mm. in 
minor diameter. At the next septum to the last these dimensions are 1] and 9 mm. 
In a large specimen the aperture is 21.5x15 mm. and at the third septum from the 
aperture 15x12 mm. This species has some similarity to Cyrtoceras camurum 
