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College of Forestry 
ORDER PULMONATA 
Famity Puysipam. 
Genus Prysa Draparnaud. 
Nos. 
42. yes ancillaria warreniana (Lea). Fig. 45, 
34, 35. 
One of the most abundant snails living in Oneida Lake, 
occurring at 28 stations. It lives in a variety of habitats 
from bouldery exposed points to protected bays filled with 
vegetation. The normal habitat, where the snail is most 
abundant and of larger size, is near the shore in shallow 
water (four to eight inches) among stones where it occurred 
in the majority of eases. In Tomahawk Lake this Physa 
occurred in either a protected bay or on an exposed shore, 
precisely as noted in Oneida Lake. The shells figured as 
ancillaria by Robertson (pl. XI, fig. 19) appear from the 
figures to belong to this race. 
This characteristic Physa seems to have been noted by but. 
few students and has doubtless been included under the all- 
embracing name of heterostropha. ‘That species, however, is 
quite different from this as will be seen by comparing 
Binney’s figure of Say’s type (Binney, 1865, p. 84, fig. 144) 
with the figures on the plate. This race is related to both 
ancillaria aud sayti (Binney, figs. 139, 136). It is much 
smaller than sayit and appears, as noted by the writer some 
years ago (F. C. Baker, 1911, p. 234), to vary toward 
ancillaria in the form of the shell, Soe becomes shouldered 
in some individuals. The surface is usually smooth and 
shining and the spiral sculpture is slight or entirely absent, 
hence its reference to heterostropha. The occurrence of this 
Physa, together with Planorbis binneyi and Lymncea stag- 
nalis lilliane, in both Tomahawk Lake, Wisconsin, and 
Oneida Lake, New York, under similar ecological conditions, 
is a striking example of the result of environmental influ- 
ences working in far separated regions on the same species. 
The same Physa has recently been observed by the writer on 
the shore of Lake Michigan at Chicago. 
