972 THE PALEONTOLOGY OF MINNESOTA. 
|[Lophospira perangulata. 
separating them. In the first place, the free whorls of L. serrulata have only four 
carine, being entirely without the uppermost or sutural keel which occurs con- 
stantly in LZ. helicteres. Then the surface striez in crossing the shell from keel to 
keel in the latter are directed very much less backward and forward than is the 
case in the former. The outer edge of the aperture is therefore quite different in 
the two species. (Compare figs. 26 and 55 on pl. LXXII.) With practice it is 
possible to distinguish them almost at a glance, and it is not by any means a hope- 
less task even when we have nothing but the casts of the interior. When the casts 
are entire at the aperture, L. servulata is recognized by the projecting angles at the 
extremities of the first and third carinze and the wide >shaped notch between them. 
When this test is not available then we must rely upon the relative distinctness of 
the carine on the upper whorls. They are recognizable much farther up on the 
spire in L. helicteres than in L, serrulata, providing, of course, the specimens are of 
equal size. | 
It is possible that the shell above described is the one which Conrad named 
M. tricarinata, but Halls figures of that species are so poor that we cannot be blamed 
if we have made a synonym. 
Formation and locality.—Stones River group, Minneapolis and St. Paul, Minnesota; Mineral Point, 
Janesville and Beloit, Wisconsin; and Dixon, Illinois. The typical form is from the Black River group 
at Pauquette’s rapids, Ottawa river, Canada. We have it also from a similar horizon in Mercer county, 
Kentucky. It is said to occur also in the Upper Buff limestone in Wisconsin. 
Collections.—Geological and Natural History Survey of Minnesota; E. O. Ulrich. 
Museum Register, No. 6858, 7360. 
LoPHOSPIRA PERANGULATA Hall. 
PLATE LXIII, FIGS. 1—7. 
Murchisonia perangulata HALL, 1847, Pal. N. Y., vol. i, p. 41, pl. X, fig. 4; not p. 179, pl. xxxyum1, figs. 
Ta, 70; SALTER, 1859, Can. Org. Rem., decade 1, p. 19, pl. Iv, fig. 7. 
Shell small, hight 10 to 20 mm.; apical angle usually about 52°, but varying 
between 50° and 57°. Volutions about six, the last inclining to become free, 
scarcely ventricose below, very gently concave above; peripheral band prominent, 
sharp, trilineate; lower carina distinct though not very prominent, sometimes very 
obscure on casts of the interior; upper slope without a carina, the gentle concavity 
extending to the suture. A small, abruptly defined umbilicus always present. 
Mouth subtriangular, slightly drawn out below. Surface markings consisting of two 
sets of strongly recurved lines of growth, one distant and sublamellose, the other 
much finer and closely arranged between the former. 
We have every reason to believe that the shell above described is identical with 
the Birdseye type of the species, but it is not the same as the Trenton form which 
