1046 THE PALEONTOLOGY OF MINNESOTA. 



(.Trochonema. 



TBOCHONEMA (s. s.), Salter. Shells turbinate and more or less widely umbilicated; 

 whorls angular, with a wide vertical peripheral band, marked off above and below 

 by a more or less sharp angle or carina; often with a third carina at the suture and 

 a fourth around the umbilicus. Aperture generally very oblique, chiefly in its lower 

 part. Type, T. umbilicatum Hall. 



EUNEMA, Salter. In every respect like Trochonema save that the shells are 

 generally higher, the umbilicus very narrow or closed entirely and the aperture very 

 little oblique. Type, E. strigillatum Salter. 



GTBONEMA, n. subgen. or gen. Whorls generally more ventricose than in 

 Trochonema, mouth only moderately oblique, umbilicus small, the surface, on the 

 lower half especially, with numerous spiral ridges among which those corresponding 

 with the two which bound the vertical peripheral band in Trochonema are sometimes 

 not easily recognized. Type, T. (G.) pulchellum, n. sp. 



Meek (Pal. Ohio, vol. i, p. 219) suggested, "at least as a subgeneric designation," 

 the name Trochonemopsis for the Devonian shell which he called T. tricarinata, 

 providing that the peritreme in this shell was really not continuous. He says of the 

 inner lip that above the umbilicus "it seems to be nearly or quite obsolete." We 

 have no evidence on the point in question, and, therefore, cannot say what should 

 be done in the matter. 



The various forms of Trochonema suggest affinities with several more or less 

 widely different genera and families. In the first place we pass by rather easy 

 gradations through Gyronema to Cyclonema. Our G. pulchellum, for instance, retains 

 many of the typical characteristics of true Trochonema. The vertical peripheral 

 band, despite the fact that it is traversed by a submedian carina, is still quite easily 

 recognized. In G. liratum it is less apparent, but in this case we have considerable 

 of an umbilical cavity, so that its relations to Cyclonema are not very apparent. In 

 G. percarinaium, however, in which the umbilicus is very small, if not entirely 







wanting, the general aspect is decidedly like Cyclonema varicosum Hall. The only 

 difference of any consequence is that the inner lip is thin and not reflected nor 

 excavated as it should be in a true Cyclonema. But we have most positive evidence, 

 showing that the development of the excavation of the inner lip was gradual in a 

 species of Cyclonema from the Stones River group in Tennessee, closely related to C. 

 varicosum, in which the inner lip is much thinner than usual and very little exca- 

 vated. In short, this and other evidence before us, is such that we are fully satisfied 

 that the best representatives of Cyclonema were derived from Gyronema. 



On pages 962 and 989 we have already expressed our conviction that Trochonema 

 and certain species provisionally referred to Lophospira are in some wise connected. 

 That this is a fact can scarcely escape any one who will compare our figures of 



