784 THE PALEONTOLOGY OF MINNESOTA. 
[Orthoceras nicolleti. 
species than are here made out. The annulated species are more readily 
distinguished by their surface variations, but among the smooth forms the exterior 
of the shell so rarely retains the surface sculpture that little basis remains for the 
determination of specific traits. No attempt is here made to follow the subgeneric 
distinctions introduced principally by Hyatt among orthoceran shells, as in the first 
place, the divisions are based largely upon variation in ornament and contour, and, 
secondly, our material is not sufficiently complete in its representation of the young 
stages to justify a subdivision of this kind. 
ORTHOCERAS NICOLLETI, Sp. nov. 
a eu 
PLATE Li, FIGS. 1-2. 4 
Tube of moderately large size, very gradually tapering, slightly arcuate in the 
original specimen, but this appears to be, to some extent, casual. Transverse section 
circular or subelliptical. Surface covered with strong, distant annulations which 
are sharp, rather narrow at the base, elevated and quite oblique in their direction, 
curving downward in traversing the shell from the convex (dorsal?) side to the inner 
side of the specimen. This obliquity increases very considerably toward the aper- 
ture. The annulations are separated by broad and deep constrictions whose width 
increases toward the aperture. Sutures transverse and even; septa regularly and 
somewhat deeply concave, crossing the shell in such a manner as to transect the 
annulations and constrictions. The interval between the septa appears to be about 
the same as that between the annulations, but this is not distinctly shown in the 
specimen, the suture and septum being clearly displayed only at the lower extrem- 
ity. The finer surface ornamentation, if such existed, is not retained. In a length 
of 145 mm. the shell bears eleven annulations, the distance between the first two on 
the outer or curved side being 11 mm., between the seventh and eighth, 15 mm. on 
the outer side, and 11 mm. on the inner. The depth of the septum exposed is 7 
mm. The diameter of the shell at its first annulation is 33 mm., at the last, 36 mm. 
This species is strikingly characterizod by its strong, oblique annulations and 
slender tube. It is, perhaps, most closely allied to the Orthoceras olorus Hall, but its 
difference in the features mentioned serve to distinguish it. 
Formation and locality.—In the Trenton limestone at Belle Creek, Minnesota. Collection of W. H. 
Scofield. 
ORTHOCERAS ANELLUS Conrad, 1848. 
PLATE XLIII, FIGS. 22—23. 
Orthoceras annellus CONRAD, 1843. Proc. Acad. Nat. Sci. Phila., vol i, p. 334. 
Orthoceras anellum HALL, 1847. Paleontology of New York, vol. i, p. 202, pl. xuut, figs. 6a-/. 
To this species are assigned two fragments of small conchs characterized by their 
very gradually expanding sides, sharp, regular, almost imperceptibly arcuate annu- 
