Baker—Molluscan Fauna of Tomahawk Lake , Wisconsin. 235 
under side of lily pads and the shell is rather flat and 
broad, while at station XYII it was found on old sticks 
in bogy swales and the shell is higher and more compressed 
than are the specimens from the two previous habitats. 
The effect of environment is quite clearly marked on the 
shells of these two diverse habitats. The ancyli were 
very abundant at all three stations. 
Family Planorbidae. 
Genus Segmentina Fleming. 
28. Segmentina armigera (Say). 
Stations II 2 , XY, XXI. All specimens were collected 
in swampy ponds. At Stations II 2 , they were found 
abundantly in the upper marshy portions of the hay. 
Genus Planorbis Muller. 
Subgenus GyraillllS Agassiz. 
29. Planorbis parvus Say. 
Stations XIY 1 , XYII. Rather rare on lily pads (Sta¬ 
tion XIY 1 ,) and dead sticks in swales (Station XYII). 
30. Planorbis hirsutus Gould. 
Stations II 2 , Y, XXI. All stations were quiet water 
habitats, and the species was fairly common in each. 
The relation of hirsutus to deflectus, albus and drapar - 
naldi is not quite clear, and perfect specimens of all these 
species are not at hand to make satisfactory comparisons. 
Deflectus is frequently spiraly striated and hirsute and any 
considerable lot of hirsutus contains specimens with a sub- 
carniate periphery. In a large series of hirsutus all gra¬ 
dations may he found between the two forms, as these are 
usually understood. The deflection of the aperture oc¬ 
curs in all the smaller planorhes and cannot he taken as a 
specific character. An examination of the types of de- 
fledtus and hirsutus in addition to a study of lots of shells 
from many localities would doubtless straighten out the 
matter. 
