GASTROPODA. 1007 
Olathrospira convexa.] 
shells. The lunule of the band are distinct, strongly curved, and crossed by a varying number of delicate 
revolving lines. Suture linear and inconspicuous except between the last two whorls of old shells. The 
last volution usually descends more rapidly than the preceding whorls. 
In casts of the interior, the condition in which this fossil usually occurs, the suture, for obvious 
reasons, is deeper than in the shell itself, the periphery of the whorls oftener rounded than flat or concave, 
and the surface markings restricted to more or less obscure impressions of the varices of growth. Even 
the molds of the exterior in the dolomitic limestone in which the species occurs so abundantly in Wiscon- 
sin and Minnesota, only in rare instances preserve any recognizable traces of the delicately cancellated 
surface sculpture. But we have never failed to detect it whenever the grain of the matrix was fine 
enough. That the surface in these specimens was originally cancellated, as shown in figure 5 on plate 
LXX, is further established by two specimens collected by one of the authors in the fine-grained upper 
member of the Stones River group at Dixon, Illinois. These specimens preserve not only portions of the 
outer layer of the shell with its beautiful markings, but here and there retain irridescent patches of the 
nacrous inner layer which, since it has been observed in so many different forms, probably pertained to all 
of the Pleurotomariide. 
We are in doubt as to the occurrence of this species in the Black River shales of Minnesota. The 
small casts usually referred here by collectors belong chiefly to our C. conica. Some of the others may 
represent ©, subconica, but we have not seen any of which we would like to say positively that it does. 
Nor have we seen a specimen in either the Clitambonites, Fusispira or Maclurea bed of the Trenton group. 
If it occurs at any of these horizons in Minnesota, it must be very rare. Casts of a species of Clathrospira 
occur in the Lorraine and Richmond groups of the Cincinnati region. They have always been regarded as 
belonging to C. subconica, but every testiferous specimen of Clathrospira that we have seen from that 
region has proved to belong to our C. conica. Though it must be admitted that the occurrence of @. 
subconica in the Cincinnati rocks requires verification, we are fully prepared to believe that many of the 
interior casts found there are really of that species, and until we know better they should be so regarded. 
Formation and locality—Stones River group, Minneapolis, St. Paul, Cannon Falls, and other 
localities in Minnesota; Beloit, Janesville, and other localities in Wisconsin; Dixon, Rockton, and Jo 
Daviess and Calhoun counties in Illinois; High Bridge, Kentucky; Lebanon and other points in Tennessee. 
Also in the Black River group at several of the foregoing localities. In Canada and New York it occurs 
in the Black River and Trenton groups, and probably also in the Hudson River group. In Ohio, Indiana 
and Kentucky, casts supposed to belong to this species occur at many localities in both the Lorraine and 
Richmond groups. 
Collections.—Geological and Natural History Survey of Minnesota; HE. O. Ulrich; W. H. Scofield. 
Museum Kegister, No. 5037. 
CLATHROSPIRA CONVEXA, 1. Sp. 
PLATE LXI1X, FIG- 51. 
Casts of the interior, the only condition in which we have observed this rare species, agree very 
closely with C. subconica in all respects save in the contour of the upper side of the volutions. This, 
instead of being nearly flat (7. e. gently convex above and slightly concave below) in the space between the 
suture and the upper margin of the peripheral band, is rather strongly conyex. The elevation of the 
band produces a narrow concavity immediately above it, but this does not greatly effect the general 
roundness of the whorls. They are more rounded than angular; in C. subconica the opposite is the case. 
The specimen figured on plate LXIX has all the appearances of being fully grown. If this is true, then 
C. conveaw is a smaller shell than C. subconica. The same specimen preserves traces of the surface sculp- 
ture. This is of a coarser pattern than that of C. subconica, there being only four or five of the transverse 
lines in 2 mm. instead of seven to ten. 
Formation and locality.—Stones River group, Calhoun county, Illinois. 
Collection.—B. O. Ulrich. 
