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, n. 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 Baphistomina. 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. 



Colkctions. E. O. Ulrich; W. H. Scofleld. 



Genus OMOSP1RA, n. gen. (Ulrich.) 



Murchisonia (part.), HALL, SALTEK 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 

 Raphistomidce, th,en 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 Pleurotomariidw, like Hormotoma bellicinda 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 Pleurotomariidcc the lunulae 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, 



