908 THE PALEONTOLOGY OP MINNESOTA. 



[Conradella triangularis. 



CONRADELLA TRIANQULARIS, W. Sp. 

 PLATE LXVII, FIGS. 19-22. 



Shell usually from 15 to 18 mm. in diameter, compressed discoid, consisting of 

 about three volutions; whorls carinate, slightly higher than wide, triangular- 

 obcordate in section, gently convex on the sides, widest and angular below where 

 the surface sinks abruptly into the umbilicus. Surface very rough, the zigzag or 

 serrated lamella; crossing the whorls almost directly, from 0.5 to 1 mm. apart, each 

 with eight or nine folds between the dorsal keel and the edge of the umbilicus; at 

 the latter the lamellae generally turn somewhat abruptly forward. Usually the 

 folds are arranged so as to present obscurely the appearances of revolving ridges. 

 At other times they may alternate in adjacent series. The angularity of the ventral 

 part of the sides of the volutions varies somewhat, the margin of the umbilicus 

 being in many cases very sharp, while in others it would be more truly described 

 as abruptly rounded. In casts of the interior, of course, the angle is never so distinct 

 as in the shell itself. 



Most collectors of northwestern fossils have identified this species with the 

 New York Trenton C. compressa Conrad, sp. They are, however, quite distinct, the 

 whorls in the New York shell being wider and more uniformly convex on the sides, 

 the umbilicus not at all sharply defined, and the transverse imbrications more 

 distant. Compared with all the known species of the genus, excepting the next, 

 which see, none seems to us so near as C. dyeri Hall sp., a variety of which occurs in 

 the Trenton of Minnesota. Still, C. triangularis is distinguished readily enough 

 from that species, as well as from all the others, by the more distinctly angular 

 character of the umbilical edge. Besides C. dyeri is a smaller shell, with rounder 

 volutions, and more sharply raised keel, while the transverse imbrications are more 

 crowded and the appearance of revolving ridges much stronger. 



Formation and locality. Vanuxemia bed of the Stones River group, Minneapolis, Minnesota, Janes- 

 vllle and Beloit, Wisconsin, and Dixon, Illinois; also at Lebanon, Tennessee. 



Confections. Geological and Natural History Survey of Minnesota; E. O. Ulrich. 

 Museum Register, Nos. 7292, 7309. 



CONRADELLA GRANDIS, n. sp. (Ulrich.) 



PLATE I.XII. FIG. 67; PLATE LXVII, FIGS. 16-18. 



This species is closely related to C. triangularis but reaches a much greater size, 

 the greatest diameter of one of the specimens being fully 30 mm. Then the trans- 

 verse section of the whorls, which also increase more rapidly in size, is a little 

 different, the dorsal slopes being more convex, the sides less angular, and the 



