DESCRIPTIONS OF NEW SPECIES. 131 



Length, five millimeters; diameter of last volution, two millimeters. 



This species is of about the same size as the recent species Pupafallax 

 Say, and closely resembles it in form and general character. 



Position and locality. Upper Green River Group; Henry's Fork, Wyo- 

 ming, where it is associated with the following species: 



Pupa arenula (sp. nov.). Shell minute, ovate; volutions five or six, con- 

 vex; suture impressed; aperture contracted; teeth of the aperture unknown. 



Length, two millimeters. 



This shell is of about the same size and shape as Vertigo ovata Say, and 

 in general aspect it closely resembles that species. It appears, however, to 

 be a true pupa; at least the characters which should separate it from that 

 genus are not apparent. 



Position and locality. Upper Green River Group ; Henry's Fork, Wyo- 

 ming. 



Genus NERITINA Lamarck. 



Nentina volvilineata (sp. nov.). Shell small, subovate in lateral outline; 

 volutions three and a half or four, regularly convex; spire short, as is common 

 in this genus, but somewhat prominent; suture slightly impressed ; aperture 

 semilunar; inner lip broad, plain, flat, its inner edge not clearly seen, but if 

 crenulated at all, it is not conspicuously so. 



Surface marked by numerous raised, revolving lines of unequal size, 

 which increase in number by implantation as the volutions increase in size; 

 the revolving lines crossed by the usual lines of growth, which give the 

 surface, upon some parts, at least, an indistinctly cancellated appearance 

 under the lens. 



Greatest diameter of the largest example discovered, nine millimeters; 

 height, lying with its aperture upon the table, five millimeters. 



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



Genus MELANIA Lamarck. 



Melania Lanmda (sp. nov.). Shell large, elongate; volutions apparently 

 eleven or twelve, uniformly increasing in size, moderately convex, bearing 

 a revolving row of prominent, strong, outward projecting, laterally sharp- 

 ened tubercles, which extend from the apex to the aperture; suture linear; 



