The Relation of Mollusks to Fish in Oneida Lake 285 
it was most frequent in shallow water in habitats sheltered 
from the waves. In the Delaware River it is subject to the 
ebb and flow of the tide, which leaves stretches of the river 
shore bare, and this fresh-water species has here been com- 
pelled to adapt itself to this periodic exposure, as have the 
marine Littorinas, and for this purpose a thick shell has 
been evolved.* The catascoptum of Oneida Lake also has a 
rather thick shell, caused probably by its normal station in 
a rough water habitat: It is widely distributed in the eastern 
part of the United States and is one of the most abundant 
snails in New York State. Listed by Beauchamp from 
Onondaga County. This snail has been observed on the 
following plants: 
Broad-leaved Arrow-head (Sagittaria latifolia). On stem. 
Pickerel-weed (Pontederia cordata). On stem. 
Water Willow (Dianthera amrericana). On stem. 
American Bulrush (Scirpus americanus). On leaf. 
Lake Bulrush (Scirpus occidentalis). On leaf. 
It has been noted feeding upon dead Water Celery leaves 
(Vallisneria spiralis) and is used as food by the Short-nosed 
Sturgeon, Common Whitefish, and Pumpkinseed. 
61. Galba emarginata (Say). Fig. 47, Nos. 1, 3. 
Observed, rarely, at four stations, always on a bouldery 
point or in a sandy, exposed bay. Nearly all of the speci- 
mens found, however, were dead shells. At Isle Royale (pp. 
60-61, 290) emarginata occurs on sandy and rocky shores 
where wave action is light; a variety, onfartoensis, is abund- 
ant in the Saginaw Bay region (p. 162) on a rocky shore 
unprotected from the waves; another variety, canadensis, oc- 
curs in the Georgian Bay region (p. 99) on rocky and sandy 
shores, in exposed situations. The distribution and interest- 
ing ecology of this species is extensively described by F. C. 
3aker (1911, pp. 408-433). Recorded by Beauchamp. <A 
variety of emarginata (variety canadensis) is eaten by the 
Common Whitefish. 
*For notes on ecology of catascopium, see F. C. Faker, 1911, pp. 387— 
388. 
