1054 THE PALEONTOLOGY OF MINNESOTA. 
[Trochonema arctatum. 
and the peripheral band is somewhat concave, while the upper slope shows a swelling in the upper half 
or a blunt ridge close to the suture and is concave for the rest. Care is required in distinguishing casts 
of this and several species of Lophospira. 
Formation and locality.—Fusispira bed of the Trenton group, Wykoff, Minnesota. 
Collection.—E. O. Ulrich. 
Trocnonema (KunemA) arcratum, n. sp. (Ulrich.) 
PLATE LXXVI, FIGS 9 and 10. 
Shell small, about 9 mm. in hight, narrow, subconical, the apical angle about 58°; peripheral band 
unusually narrow, about half as wide as the upper slope, pitching inward, the upper margin being more 
prominently angular or keeled than the lower; upper slope slightly concave in the lower half and convex in 
the upper; base depressed convex, umbilical perforation small but distinct; aperture not very oblique, 
subovate, rounded on the inner side, higher than wide. The lines of growth are very fine. As near as 
they can be made out, they cross the whorls at about the same angle as in 7. robbinsi. 
The peripheral band is so narrow that the shell is very apt to be mistaken for one of the Pleuwroto- 
martvide. Sardeson describes a Pleurotomaria clivosa from the Black River shales at Minneapolis that looks 
so much like 7. arctatum that we suspect it belongs to this genus. 
Formation and locality.—Upper part of Trenton group, near Burgin, Kentucky. 
Collection. —E. O. Ulrich. 
TrocHoneMa (KuNEMA) oBsoLETUM, ». sp. (Ulrich.) 
PLATE LXXVI, FIGS. 6—8. 
Excepting the body whorl, this small shel! would differ from 7. arctatum only in being a trifle wider 
but with the last whorl! it assumes a very different expression. The last whorl namely is relatively quite 
rounded, the upper slope being inflated and the base somewhat ventricose, while between the two the 
peripheral band is scarcely distinguishable. The lines of growth, while extremely delicate on the upper 
whorls and still fine on the iast, are nevertheless much stronger here. with now and then a wrinkle that 
is distinctly visible to the naked eye. The axis seems not to be perforated, the central part of the base 
being merely sunken in. 
Formation and locality —Upper part of Trenton group, near Burgin, Kentucky. 
Collection.—E. O. Ulrich. 
Subgenus (?genus) GYRONEMA, Ulrich. 
This group of species occupies an intermediate position between the true 
Trochonemas and Cyclonema. (See remarks and definition pp. 1045 to 1047.) As we 
believe the division is important and well founded in nature, we shall employ it 
here in the sense of a full genus. 
‘ 
GYRONEMA PULCHELLUM, %. Sp. 
PLATE LXXVIII, FIGS, 19—21. 
Shell small, 9 to 17 mm. in hight; greatest width of body whorl, which constitutes much the greater 
part of the shell, equalling about three-fourths of the hight; apical angle about 85°. Whorls six and a 
half in an éntire shell, the first two minute, rounded, glassy, and perfectly smooth, the third gradually 
assuming the angles of the following turns. Body whorl divided into three subequal regions; first, the 
