56 
glaciation, split up into many varieties, more or less distinct, reflecting the 
influence of the diverse lake environments. Mozley records variety striatus 
F. C. Baker from several places in Manitoba, but this is rather the form 
recently differentiated as variety sayi F. C. Baker, the modern descendant 
of the fossil striatus. ( See Moll. Wis., I, p. 322, for the reasons for this 
change.) No typical striata have been seen from the recent fauna. Whether 
the typical form is found in the rivers of Canada is not definitely known to 
the authors, no such material having been seen from the area under con- 
sideration. Several of the northern varieties — percarinata Walker, shellen- 
sis F. C. Baker, eahni F. C. Baker— should be found in some one of the many 
lakes of northern Ontario. 
Helisoma (Pierosoma) trivolvis (Say) 
Pashkokogan, Cat, and Bamaji lakes; outlet of lake Bamaji. 
The specimens of trivolvis from this area are large, fine examples of 
the species, showing some variation, however, in sculpture as well as in 
relative axial height of the body whorl. The material from the outlet of 
Bamaji lake, living on rocks in rapid water, shows a tendency to increase 
the axial height as in the race pilsbryi , but it is without doubt referable 
to trivolvis. True pilsbryi is apparently rare in northern Canada. 
Whiteaves records trivolvis from 2 miles above mouth of Harricanaw 
river, Hannah bay, from Ozhiski, Machaw r aian, and Wapikopa lakes, 
Attaw'apiskat and Winisk rivers, Ontario. Dali cites English river and 
Moose Factory. Mozley cites many localities in Manitoba. The species 
is known to extend geographically as far north as Great Slave lake and it 
doubtless exists still farther to the north. 
Helisoma (Pierosoma) trivolvis pilsbryi (F. C. Baker) 
Planorbis binneyi Authors, not Tryon. 
Marchington river; Sturgeon lake, Rainy River district. 
Specimens from these localities are referable to pilsbryi, which appears 
to be rare in Canada. Some of the material recorded as either trivolvis or 
corpulenta may have been of this race. The Planorbis binneyi recorded by 
Mozley from Manitoba is referable to pilsbryi, binneyi being restricted to 
the Pacific Coast region. 
Helisoma (Pierosoma) corpulenta (Say) 
St. Joseph, Birch, Hill, Bamaji, Abram, and Blackstone lakes; March- 
ington river. Trout lake near International Boundary, Rainy River dis- 
trict; Knife lake, St. Louis county, Minn. 
One of the rarest of freshwater species and practically unknown until 
recently, this fine planorbid is now known to be one of the most abundant 
species of the northern fauna, wddely distributed from the International 
Boundary to Athabaska, in latitude 56° 30'. It is unknown at present 
outside of the Hudson Bay drainage and in the United States has not been 
reported authentically south of northern Minnesota near the International 
Boundary. The records of this species, as far as known, are as follows: 
Minnitaki lake and lac Seul; Root and English rivers; English river below' 
Manitou fall; Knee lake (Whiteaves); Knee lake, Isle La Crosse lake, 
English lake, Rat portage (Dali, Walker); lake Simcoe to Rainy lake, 
Lake of the Woods, Winnipeg river and lake, to Vermilion lake, Athabaska 
