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.) 
* G:00 5." 10.50; P: 3 BeOS Sr 4,00 “ (8397.) 
a ODE fo 9° 11.00; < ‘: 6:5055>\" 4.00 * (8397.) 
Ammal: 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. 
long, 2.00 mill. wide, small specimen); head broad, auriculated; 
respiratory tube very large. 
Jaw: As in ¢rivolvis. 
Radula formula: 42+28+44+44+44+34+13 (22—1—22); the 
teeth seemed to be in all respects like “#ivolvis. 
Gemtalia: 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, III. (Baker). 
Geological distribution: Pleistocene. 
Habitat: Found under conditions similar to P. ¢rivolvis. 
Remarks: This seems to be a very distinct species and is 
quite rare. While examining young specimens of ¢r7volvis the 
writer was struck by the very close similarity between them and 
truncatus. his fact leads him to believe that the present spe- 
cies is a recent offshoot or variation from ¢vivo/vis, 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 
. 
