IS 
and thickened, white, a wide white callus covering the parietal wall; the 
aperture is purplish within. 
H. 12*0; Or. diam. 26-5; Ap. H. 11*5; D. 7*5 mm. Lake Nipigon (re Whiteaves, 
N.MC. 2093). 
H. 11*0; Gr. diam. 23*6; Ap. H. 10*0; D. 8-0 mm, Lake Nipigon (re Whiteaves, 
N.M.C. 2093). 
H. 12*1; Gr. diam. 26-1; Ap. H. 11-0; D. 8-0 mm. Bayfield, Wis. (U.I. Z13677). 
H. 12-2; Gr. diam. 28-0; Ap. H. 11-0; D. 8-0 mm. Bayfield, Wis. (U.I. Z13677). 
H. 13-5; Gr. diam. 29-0; Ap. H. 12-5; D. 9-0 mm. Outlet Bamaji lake (U.l. 
Z30857), 
H. 14-9; Gr. diam. 28*0; Ap. H. 13*8; D. 10 0 mm. Outlet Bamaji lake (UJ. 
Z30857). 
Type Locality. Ponds near Mile-end Toll Gate, Montreal, Canada. 
Types. National Museum of Canada (Mollusca), lectotype 3869, 
paratypes 3870. 
Macrostomum has been considered a synonym of trivolvis by nearly all 
students of freshwater molluscs, including the writer (Moll. Wis., p. 331). 
Dali (Alaska Moll., p. 89) considered it a recognizable variety and it is 
sufficiently distinct to constitute a rather characteristic geographic race 
of trivolvis. The shell is much larger, the whorls swollen, and the axial 
height much greater, the aperture is larger, higher than wide, and the lip is 
notably expanded and reflected. Anatomically, the radula formula is 
30-1-30 to 35-1-35, whereas in trivolvis it is never more than 26-1-26 and 
the average is 24-1-24. There are many forms that appear to connect 
macrostomum with trivolvis, which if absent would lead the most careful 
student to give the large form specific rank. In Michigan and Wisconsin, 
and even in the northern part of Ohio, there are large, trivolvis~Yike shells 
that appear to be intermediate between the two forms. Specimens from a 
pond near Presqu’ile harbour, Huron county, Mich., are of this nature and 
some of the larger individuals would certainly be identified as macrostomum 
if found without the transition specimens. Two specimens are figured on 
Plate III, figures 17, 20. 
Macrostomum is widespread geographically. It has been personally 
identified from the following places: 
Lake Nipigon, Ontario (Nat. Mus., Canada, 2093), Ojiski lake, Attawapiskat (2220), 
Wapikapa lake, Winisk river (2218, 2219), Machawaian lake, Attawapiskat (2216), 
Wintisk river. The last five lots were collected by Mclnnes. Also collected from a 
lake northwest of Cormorant lake, Manitoba (2309), Mclnnes collector. It is in the 
University of Illinois Museum from: beach pond north of Bayfield, Bayfield county, 
Wis., and Pike creek, near Salmo, Bayfield county (Z13677, Z13395), collected by 
F. C. Baker; Yellow river, near Spooner, Washburn county, Wis. (Z18524), collected 
by F. C. Baker; Aroostook county, Maine, several localities (Z32480, Z32481), 
collected) by O. O. Nylander; Pashkokogan lake (Z30860, 30861), outlet Bamaji lake 
(Z3Q856, 30857), Bamaji lake (Z30858), Cat lake (Z3G859), all western Ontario, 
collected by Dr. A. R. Cahn. The US. National Museum contains three lots: Lake of 
the Woods, northwest angle of Minnesota, collected by W. F. Kubiehek of the U.S. 
Biological Survey (347753); Lake of the Woods, Warroad, Minn., collected by 
Metcalf of the Biological Survey (347783) ; and Cross Lake thoroughfare, Aroostook 
county, Maine, collected by W. C. Kendall (187682). In the Royals Ontario Museum 
of Zoology this race is represented from the following localities: lake Abitibi Ontario, 
collected by J. L. Hart (1663, 1671); Georgian bay, Ontario, collected by A. D. 
