908 THE PALEONTOLOGY OF MINNESOTA. 
LConradella triangularis. 
CoNRADELLA TRIANGULARIS, ”. 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 lamelle 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 lamelle 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- 
ville and Beloit, Wisconsin, and Dixon, Illinois; also at Lebanon, Tennessee. 
Collections.—Geological and Natural History Survey of Minnesota; E. O. Ulrich. 
Museum Register, Nos. 7292, 7309. 
CoNRADELLA GRANDIS, n. sp. (Ulrich.) 
PLATE LXII, 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 3) 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 
