166 ILLINOIS ACADEMY OF SCIENCE 
55. P. gyrina Say—In all ponds and streams visited, in all 
three counties,—a most prolific and active species, probably the 
commonest of all gastropods. It is found on stones, twigs, 
aquatic plants, in slow running water, stagnant pools, ponds, 
rapid streams, temporary pools, at times in damp places far 
from bodies of water. It endures dessication. In January, 
1909, I found it crawling on the under side of ice at Crystal 
Lake. 
56. P. sayii Tappan—Urbana, Champaign Co., Dr. Frank C. 
Baker det. The specimens are in the collections of the Ill. 
State Lab. Nat. Hist. Excepting for warreniana, I found no 
Physa which approached sayii. 
GENUS APLEXA “Fleming” Sowerby, 1822 
57. A. hypnorum Linnzeus—Muncie, Vermilion Co., in 
slowly moving or pounded waters, usually on plants or debris, 
under leaves, or on the muddy bottoms. It endures much des- 
sication. 
Family Ancylide _ 
Subfamily Ferrissiinze Walker, 1917 
GENUS FERRISSIA Walker, 1903 
Subgenus Lzevapex Walker, 1903 
58. F. kirklandi Walker—Salt Fork, Crystal Lake, and Ur- 
bana, Champaign Co. Found in great abundance on stems and 
the under sides of leaves of water lilies. The water of the lake 
was ponded since the dredging of the Salt Fork; this limpet 
was not found prior to the ponding of the waters of this lake. 
F’. tardus was the only form found prior to this, but after the 
dredging of the Salt Fork, tardus disappeared completely and 
was replaced by kirklandi. Gundlachia meekiana, present in 
the lake before its waters became ponded, also disappeared. 
(Subgenus Ferrissia Walker, 1903) 
59. F. rivularis Say—White Heath, Piatt Co., Salt Fork, 
Urbana, Champaign Co., on sticks and plants. At White 
Heath, Piatt Co., Salt Fork, Urbana, Champaign Co., on sticks 
and plants. At White Heath it was found in a small stream 
near the Sangamon River, attached to rocks where the current 
was the strongest. In the Salt Fork also, it sought places of 
swift current. 
