134 INVERTEBRATE PALEONTOLOGY. [WHITE. 



to any other established genus and is accordingly referred to it provision- 

 ally. 



Position and locality. Bitter Creek Group ; Black Buttes, Wyoming. 



Genus TULOTOMA Haldeman. 



Tulotoma Thompsoni (sp. nov.). Shell moderately large, having the 

 general form of shells of this genus; spire elevated, its sides broadly convex; 

 volutions six or seven, their outer side flattened or only slightly ^convex ; 

 proximal side of the last volution also flattened or slightly convex, produc- 

 ing a more or less prominent revolving angle between them; suture linear 

 or faintly impressed ; umbilical chink minute or wanting. Surface of the 

 three or four first volutions of the spire convex and unmarked, except by 

 the ordinary lines of growth, but the last two or three volutions are con- 

 spicuously marked by prominent tubercles in two or three revolving rows, 

 extending to the aperture, and which sometimes seem to be connected in 

 their respective rows by slightly raised revolving lines. .The distal row of 

 tubercles is strongest and is situated near the suture, on its proximal side. 

 The proximal row is immediately upon the distal side of the suture, the 

 tubercles of which are more elongated transversely than the others, but not 

 so prominent. Between these two rows there is sometimes another obscure 

 one, but upon some shells it is reduced to only a raised line. 



Length of a large example, thirty-eight millimeters ; diameter of the 

 last volution, twenty-five millimeters. 



This shell resembles the recent species T. magnified Conrad, but differs 

 from that shell in its more convex volutions, its faintly impressed suture, and 

 the different arrangement of its tubercles. It also resembles T. ( Viviparits} 

 Strossmayeriana Pilar, as published by Brasilia, but differs in the less con- 

 vexity of its volutions, especially the proximal side, and in the different 

 character and position of the tubercles that adorn its surface. 



Genus PHOKUS Montfort, 



Phorus exonerates (sp. nov.). Shell small, concavo-convex, the convexity 

 of the upper side being slight and nearly uniform ; volutions one and a half 

 or two; suture not distinctly shown; surface apparently quite plain or marked 



