1054 THE PALEONTOLOGY OF MINNESOTA. 



[Trochoneiua 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. Fusisplra bed of the Trenton group, Wykoff, Minnesota. 

 Collection. E. O. Ulrich. 



TROCHONEMA (EUNEMA) ARCTATUM, n. sp. (Ulrich.) 



PLATE LXXVI, FIGS 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 slops, 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 T. robbinsi. 



The peripheral band is so narrow that the shell is very apt to be mistaken for one of the Pleuroto- 

 mariidce. Sardeson describes a Pleurotomaria clioosa from the Black River shales at Minneapolis that looks 

 so much like T. arctatum that we suspect it belongs to this genus. 



Formation and locality. Upper part of Trenton group, near Burgin, Kentucky. 

 Collection. E. O. Ulricb. 



TROCHONEMA (EUNEMA) OBSOLETUM, n. sp. (Ulrich.) 



PLATE LXXVI, FIGS. 6-8. 



Excepting the body whorl, this small shell would differ from T. 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 last, 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 Cyclonerna. (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. 



GYRONKMA PULCHELLUM, n. sp. 



PLATE LXXVIII, FIGS. 19-21. 



Shell small, 9 to 17 mm. in liL'ht: 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 entire 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 



