22 
of the basal whorls. In the Georgian Bay lot, however, there are some 
specimens with the body whorl rounded on the base, although the inner 
whorls are subangulated or even angled. These connect perfectly with the 
Rideau River shells which have a rounded body whorl with subangulated 
inner whorls. These shells show considerable variation in this respect, but 
the inner whorls appear to be invariably carinated as in the Basswood River 
and Georgian Bay shells. In some of the Canadian lakes both infracarina- 
tum and corpulentum multicost atum occur and the two forms are difficult 
to distinguish in the case of some adult shells. Thus the two forms occur in 
Bamaji lake and in lac des Mille Lacs swamp. An examination of the 
young or very immature specimens will invariably separate the two species, 
that of multicostatum having a sharp carina encircling the basal whorl, 
whereas this part of the shell is rounded or but slightly angulated in 
infracarinatum. This feature is well shown on Plate IV, figures 20 and 21. 
The radula formula of the several lots referred to infracarinatum is shown 
below; Basswood river, 33-1*33 to 38-1-38; Rideau river, 34-1-34 to 
37-1-37; Bamaji lake, 31-1-31 to 38-1-38; lac des Mille Lacs swamp, 
30-1-30 to 37-1-37. 
The geographic distribution of this species appears to be extensive. 
The material examined is as follows: 
Nat. Mus., Caaada, many localities in Rideau river; U.S. Nat. Mus., Rideau river, 
collected by F. R. Latchford (120987, 251144, 346625, 361736); Mus. Nat. Hist. U.I., 
Basswood River rapids (types); marshy area on Toad island, Georgian bay, collected 
by Dr. R. C. Rush (Z25258) ; Marchington river, Kenora district (Z3085O) ; Bamaji 
lake (Z32342, 32343), Blackstone lake (30868), Trout lake (Z32363), Patricia portion of 
Kenora district; lac des Mille Lacs swamp, Thunder Bay district (Z32335) ; all 
collected by Dr. A. R. Cahn. The Baker collection contains a lot of infracarinatum 
from Thousand Island park, St. Lawrence river, N.Y. (852). These were previously 
referred to binneyi. 
The collection of the U.S. National Museum contains two lots 
apparently referable to infracarinatum. One from isle La Crosse, English 
river, collected by Robert Kennicott (29231), and one from Knee lake, 
western Ontario, collected by E. A. Preble (180279). These shells were 
previously referred to corpulentum by Dali (Alaska Moll., p. 87) but are 
not that species. Both are characterized by great axial height and ex- 
panded aperture. A specimen from Knee lake measures H. 14*0; Gr. diam. 
23*6; Ap. H. 14*5; D. 8 •1 mm. The height of the expanded aperture is 
16 mm. It is desirable that more specimens of this form be examined, 
especially the radula, as it might constitute a variety of infracarinatum. 
The lower whorls are not as distinctly carinated as in that species but more 
so than in pilsbryi. 
In the American Museum of Natural History, two specimens occur in 
the Jay collection, one marked Winnipeek river, and labelled corpulentus 
(6222) ; another specimen, half grown (11133) is without locality, but 
labelled corpulentus. A specimen in the Cooke collection, 15576, from 
* lake Superior/ labelled corpulentus, is infracarinatum. Three specimens 
in the Stewart collection from Winnipeg river are infracarinatum. 
A specimen in the collection of the Zool. Mus., Univ. Mich. (49737) 
from Wabamun lake, Alberta, has a w*ide, flaring aperture and heavily re- 
