DESCRIPTIONS OF NEW SPECIES. 109 



Genus ARCILEOCIDARIS McCoy. 



Arcliceocidaris cratis (sp. nov.). Spines slender, gradually tapering from 

 base to point; shaft ornamented with sharp, distant spinules, each about one 

 and a half millimeters long and pointing strongly upward ; basal ring promi- 

 nent, plain, except the fine crenulation of its edges, and situated very near 

 the proximal end of the spine. Surface apparently smooth. 



Length about six centimeters; diameter just above the basal ring 1 nearly 

 three millimeters; diameter of basal ring about four millimeters. 



The collections of the Geological Survey of Nebraska in the cabinet 

 of the Smithsonian Institution contain a single spine of this species, which, 

 together with that of these collections, is all that is known of the species. 

 It may be readily recognized by its smooth, slender shaft, with its distant, 

 sharp spinules. 



Position and locality. Lower Aubrey Group; confluence of the Grand 

 and Green Rivers, Utah. 



Mollusca. 



Gasteropoda. 



Genus ^NATICOPSIS McCoy. 



Naticopsis remex (sp. nov.). Shell of ordinary size, very oblique when 

 adult, by the elongation and enlargement of the last volution ; volutions 

 about four, convex, increasing rapidly in size, the last one large and much 

 produced ; spire small and short ; suture impressed. Surface marked by 

 the usual lines of growth, and, although that of the specimens in the collec- 

 tion is not very well preserved, there are some indications of the presence 

 of faint revolving striae also. 



Length across the longest diameter of the aperture and body volution 

 of an average-sized specimen, twenty-three millimeters ; short diameter of 

 the same, seventeen millimeters. 



Position and locality. Summit of the Lower Aubrey Group ; confluence 

 of the Grand and Green Rivers, Utah. 



