DESCRIPTIONS OF NEW SPECIES. 133 



Length, about five millimeters ; diameter of the last volution, nearly 

 two millimeters. 



Position and locality. Bitter Creek Group ; west base of Mu-si-ni-a 

 Plateau, 1,000 feet below the summit, Utah. 



Genus VIVIPARUS Montfort. 



Viviparus plicapressus (sp. nov.). Shell rather under medium size ; 

 spire, cqnical ; sides nearly straight ; volutions about seven, convex, the 

 outer and anterior convexity of the last one continuous and uniform ; suture 

 impressed. At the distal side of each volution there is a small, more or less 

 distinct, revolving groove or furrow, by which that part is folded and closely 

 appressed against the proximal side of the adjacent volution, the fold form- 

 ing a slight projection upon the proximal side of the suture. Surface 

 marked by the ordinary lines of growth, and upon some examples there 

 appears a faintly raised revolving line or incipient angulation near the 

 middle of the outer side of the volutions. 



Length, about twenty-five millimeters ; breadth of last volution, twelve 

 millimeters. 



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



Genus LEIOPLAX Troschel. 



Leioplax f tiirricula (sp. nov.). Shell of ordinary size, elongate conical ; 

 volutions about eight, gradually increasing in size ; convex angular, the 

 angle being sharp, prominent, and situated a little in advance of the middle 

 of the side of the volutions of the spire ; suture slightly impressed ; last 

 volution broadly rounded from the revolving angle to the umbilicus ; umbil- 

 icus narrow, deep and marked within by two or three revolving lines. Sur- 

 face upon both sides of the revolving angle of the volutions marked more 

 or less distinctly by two or three revolving raised lines. 



Length, thirty millimeters ; diameter of last volution, fifteen millime- 

 ters. This shell has the aspect of some forms of Goniobasis, but the presence 

 of an umbilicus excludes it from that genus. It also varies from the 

 typical forms of Leioplax, but appears to be more nearly related to this than 



