1056 THE PALEONTOLOGY OF MINNESOTA. 



[Gyroncma llratum. 



least one prominent keel in the middle of the peripheral band. Occasionally this median keel is double, 

 as in flg. 22, or there may be a smaller carina between it and the lower peripheral keel, as in flgs. 23 and 

 24. The lines of growth are rather obscure on our specimens, but apparently they are not as fine nor as 

 regular as In G. pulchellum. The duplication of some of the carinas is a peculiar feature. 



This species is generally identified with Hall's Pleurotomaria percarinata, an upper Trenton shell 

 from New York that is now commonly referred to Cyclonema. Assuming that Hall's figure of his type 

 specimen (toe. at.) is correct, we would say that the northwestern form above described cannot possibly be 

 the same species. 



Formation and locality. Stones River group, possibly also Black River group, at Beloit and other 

 localities in Wisconsin, and Dixon, Illinois. We are informed that it occurs at Minneapolis and St. Paul, 

 but have not succeeded in obtaining it from any point in Minnesota. 



Collections. University of Wisconsin; E. O. Ulrich. 



GYRONEMA LIRATUM, n. sp. 



PLATE LXXVI1I, FIGS. 14-16. 



The peculiarities of this fine species are very well shown in our illustrations. It is related to (?. 

 pukhelluni and G. duplicatum, but is distinguished at once from both by its much larger umbilicus and 

 more rapidly spreading and rounder volutions. The specimen is a cast, partly of the exterior and partly 

 interior. The former shows about fourteen revolving carinae and thick lines on the last volution, among 

 which the two which correspond with the upper and lower boundaries of the peripheral band in other 

 species are distinguished with some difficulty. They are a little stronger than the others excepting one 

 equally strong and a trifle more prominent which lies midway between them. Only these three are indi- 

 cated on the interior of the body whorl. 



Formation and locality. Stones River group, Beloit, Wisconsin. 

 Collection. E. O. Ulrich. 



Genus CYCLONEMA, Hall. 



In part rieurotomaria of CONKAD and HALL. 



(Jyclonema, HALL, 1852, Pal. of N. Y., vol. ii, p. 89; SALTEU, 1859, Can Org. Rem., Dec. 1, p. 23. Not 

 Cyclonema, (HALL) LINDSTROM, 1884. Sll. Gast. and Pter. of Gotland, p. 174 



Shell turbinate or conical, never thick, composed of few more or less ventricose 

 whorls; no umbilicus; surface sculpture consisting of numerous revolving lines and 

 small ridges crossed obliquely by sharp lines of growth; aperture oblique, varying 

 from rounded to subquadrate; inner lip more or less thickened, reflected, always 

 excavated. Types, C. bilix Conrad and C. mediate Ulrich. 



The principal characteristic of this genus is the excavation of the inner or 

 columellar lip. This peculiarity distinguishes the genus at once from Gyronema 

 which includes some otherwise not very different shells. In Strophostylus there is a 

 fold on the inner lip, forming a similar excavation, but it is generally so much 

 twisted that its upper end is not visible in a direct view of the mouth. As a rule 

 also the inner lip is much thicker than in Cyclonema. It seems a little strange that 

 the relations of Cyclonema and Strophostylus have not been recognized heretofore. 

 They are certainly very closely related and in practice it is often difficult to 

 distinguish them. But if we are correct in deriving Cyclonema from Gyronema then 



