9O LAND AND FRESH WATER MOLLUSKS 



stretching westward with the Yukon drainage ! I have never seen any 

 specimens corresponding exactly to Tryon's figure of P. hornii, but 

 the variations I have seen of P. subcrenatus often approach it so 

 closely that I have little doubt of their identity. P. macrostomus 

 seems, from an examination of the types, to be a form of trivolvis 

 which has survived a year longer than usual, in a locality where it was 

 not stinted in lime, resulting in a remarkably fine shell with richly 

 colored aperture. 



Planorbis (Planorbella) campanulatus Say. 



Planorbis campanulatus SAY, Journ. Acad. Nat. Sci. Phila., n, p. 166, Jan., 

 1821 (Cayuga Lake, N. Y.). HALDEMAN, Mon. Limn., p. 9, pi. i, 

 figs. 7-1 1, 1844. 



Planorbis bellus LEA, 1844 (immature shell) -+- P. complanatus Miller Christy, 

 1885. 



Range. The type: New England to Tennessee, Florida and 

 northward ; Anticosti Island ! Lake Superior to the Saskatchewan ; L. 

 Winnipeg, Red River of the North, Nelson and English Rivers ; 

 Moose Factory ! Great Slave Lake, N. Lat. 62 ; Lake 

 of the Woods ! 



Variety rudentis : Knee Lake, Hayes River, Kee- 

 watin, N. Lat. 55 (E. A. Preble) ! 



This well known species is confined to the Atlantic, 

 Mackenzie, and Hudson Bay watersheds, and has not 



been reported north of Great Slave Lake. So far 

 orbis campanu- 

 latus Say. as t ^ ie specimens examined go to show, it is rather re- 

 markably uniform in its characters, the number of 

 whorls remaining always about the same, though the actual size 

 varies with the food supply and healthfulness of the environment. 



A form which may prove distinct, or a variety of this species, was 

 collected by Mr. Preble at Knee Lake. The comparative measure- 

 ments are : 



Whorls. Major Diam. Minor Diam. Axis. 



Type. 4.75 15.0 mm. n mm. 6.5mm. 



Variety. 5.25 17.5 14 6.0 



Very similar specimens were obtained from Anticosti Island and 

 from Marl Lake, Michigan, in which the coil is even more irregularly 

 wound, a condition I take to be pathological. The most noticeable 

 difference, after the axially shorter whorls and larger size, is in the 

 umbilicus, which in the variety is, as it were, reamed out, exhibiting 

 three and a half whorls ; while in the more compact type the umbilicus 

 when examined w r ith a lens shows only two and a half whorls, which 



