The Relation of Mollusks to Fish in Oneida Lake 277 
It is beheved to feed on filamentous algze, desmids, and 
diatoms, and is eaten by the Short-nosed Sturgeon. 
49. Planorbis trivolts Say, variety. Fig. 46, Nos. 19-20. 
A form of ftrivolvis occurs at five stations, where the 
habitat is not as protected as those occupied by typical 
trivolvis, several of them, as V and XXX, 2, being fully 
exposed to wave action. The shell is smaller than trivolvis, 
the whorls are wider and the shell in general seems to stand 
midway between trivolvis and binneyt. Walker has expressed 
the opinion that binneyt is a variety of trivolvis and the 
presence of these intermediate forms seems to point in that 
direction. This may be the form ealled lentus by New York 
conchologists and listed as such by Beauchamp. This 
Planorbis has been observed on the following plants: 
Broad-leaved Arrow-head (Sagit- Lake Bulrush (Seirpus occiden- 
taria latifolia). talis). 
Pickerel-weed (Pontederia cor- American Bulrush (Scirpus ameri- 
data). canus). 
Water Willow (Dianthera ameri- Green filamentous alge. 
cana). 
50. Planorbis binneyt Tryon. Fig. 46, Nos. 17-18. 
This handsome Planorbis was noted at seven stations, the 
habitat always being a more or less exposed bouldery point 
or bay. <A favorite location was noted to be at the shore 
edge, in a few inches of water, the snails feeding on the 
ereen alex on the rocks. This species was noted in Toma- 
Hawk Lake in both sheltered bays and on exposed shores. It 
is an abundant species, extending from Massachusetts west 
to Oregon (F. C. Baker, 1911, p. 287). It has been identi- 
fied by local conchologists as a wide form of frivolvis. It is 
not in Beauchamp’s list and has not been recorded in any of 
the catalogs of New York shells. 
51. Planorbis antrosus Conrad. Fig. 47, Nos. 17-20. 
This Planorbis, long known under the name _ of 
bicarinatus (which is preoccupied), was obtained from ten 
