THE NATURAL HISTORY SURVEY. 291 



brownish; surface shining, lines of growth numerous, vertical, 

 raised, equidistant, crossed by raised, equidistant spiral lines, 

 giving the surface a latticed aspect; these spiral lines are de- 

 veloped on the lower, rounded surface and on the peripheral 

 portion of the whorl, but not on the flat upper surface; apex 

 distinct, pearly, a little raised above the whorls; whorls four, 

 carinated above, subcarinated below; periphery rounded; spire 

 flat, as though cut off, exhibiting all the volutions in the same 

 plane; sutures separated by a raised carina; base of shell 

 rounded, last whorl strongly keeled; umbilical opening round, 

 wide, rather deep; aperture ovate, deflected and rounded at the 

 lower part, flat and shouldered at the upper part; peristome 

 thin, acute, not expanded, thickened by a heavy, white callus 

 on the inside, which is bordered by a purplish band; interior of 

 aperture whitish, showing the spiral and growth lines. 

 Length, 6.00; width, 11.00; aperture length, 6.00; width, 5.00 mill. (8397.) 

 6.00; " 10.50; " " 5.50; " 4.00 " (8397.) 



7.00; " 11.00; " " 6.50; " 4.00 " (8397.) 



Animal: Brownish in color, lighter on sides of foot and 

 tentacles; tentacles one-half the length of foot, rather thick 

 and blunt; foot wide, short, rounded at both ends (4.50 mill. 

 Jong, 2.00 mill, wide, small specimen) ; head broad, auriculated; 

 respiratory tube very large. 



Jaw: As in trivolvis. 



Radula formula: P+f+m+i+f +** (22- 1-22); the 

 teeth seemed to be in all respects like trivolvis. 



Genitalia: Not examined. 



Distribution: Saginaw Bay, Mich. (Miles); - Elk River, 

 Antrim County, Mich. (Walker); Miller's, Ind. (W. K. Higley); 

 North Branch Chicago River (T. Jensen); George Lake (T. 

 Jensen); Chicago Drainage Canal, Summit, 111. (Baker). 



Geological distribution: Pleistocene. 



Habitat: Found under conditions similar to P. trivolvis. 



Remarks: This seems to be a very distinct species and is 

 quite rare. While examining young specimens of trivolvis the 

 writer was struck by the very close similarity between them and 

 tmncatus. This fact leads him to believe that the present spe- 

 cies is a recent offshoot or variation from trivolvis, which is the 

 parent stock. The truncated spire and latticed sculpture serve 

 to distinguish this very beautiful species. It seems to be an 

 inhabitant of deep water and only a very few specimens have 

 thus far been collected in this area. The animal is very slow 



