944 THE PALEONTOLOGY OF MINNESOTA. 
[Raphistomina rugata. 
Formation and locality—Lower division of the Stones River group (Safford’s Central limestone), 
near Murfreesboro, Tennessee. It is here associated with a broadly umbilicated and much larger species, 
apparently of this genus, of which, unfortunately, we have so far failed to secure satisfactory examples. 
Several other discoidal shells occur at this locality rendering great caution a necessity in discriminating 
between them. 
Collection —E. O. Ulrich. 
RAPHISTOMINA RUGATA, #. Sp. 
PLATE LXVIII, FIGS. 10—13. 
This pretty species differs in at least two respects from all of the foregoing 
species. First, the surface markings are relatively stronger, second, the umbilicus 
is more sharply outlined. As usual the surface markings are faint in the umbilicus 
and near the suture line, and much stronger in the peripheral portion of the shell. 
The umbilicus is rather larger than the average, its diameter equalling about a 
fourth of the entire width of the shell. Another peculiarity is that the upper surface 
of the whorls is almost flat from the but slightly impressed suture line to the edge; 
nor is there more than a barely perceptible concavity beneath the edge. Often the 
whole upper surface of the shell is perfectly flat, giving it more of the usual 
appearance of a Raphistoma than a Raphistomina. The spire is always lower than in 
any of its congeners, and in no observed case higher than in fig. 12. 
Formation and locality.—Clitambonites bed of the Trenton group at various localities in Goodhue 
county, Minnesota. 
Collections.—EK. O. Ulrich; W. H. Scofield. 
Genus OMOSPIRA, n. gen. (Ulrich.) 
Murchisonia (part.), HALL, SALTER and BILLINGS. 
For generic characters see page 932. 
We are anything but satisfied respecting the systematic position of this genus. 
If Scalites, Emmons, could be proved to possess the essential characteristics of the 
Raphistomide, then we would have an undeniable link between Omospira and 
Raphistoma. In the absence of such a link, the general resemblance which Omospira 
bears to certain Pleurotomariide, like Hormotoma bellicincta and Eotomaria elevata, 
gives us not a little trouble to explain away in a convincing manner. Still, there 
are two features about the sinus in the upper lip and the band-like space resulting 
from it in the growth of the shell that are anything but indicative of pleurotomarian 
affinities. First, the great width of the band, and second, the oblique,—perhaps it 
would be better to say the outwardly increasing,—curvature of the lines crossing it. 
In all true Pleurotomariide the lunule or lines crossing the slit-band, providing the 
latter does not lie, as in Liospira micula, partly over the peripheral edge, form a 
uniform curve in passing from one to the opposite border of the band. (See fig. 13, 
