161] FAUNA OF BIG VERMILION RIVER—BAKER 63 
been observed in other places, notably in the Genesee River, at Rochester, 
N. Y., where sewage pollution was at one time very severe, that these 
pulmonate water snails were the last to succumb to the toxic influences 
of pollution and they have been known to live in water that was filled 
with putrescent matter and also in water strongly impregnated with arsenic. 
When these snails begin to disappear, conditions must indeed be deplorable. 
FAMILY ANCYLIDAE 
53. Ferrissia rivularis (Say). River Limpet. 
The tiny limpet-like shell known as Ancylus (Ferrissia) rivularis was 
very abundant in parts of Salt Fork, its usual habitat being the inside of 
empty valves of the naiades. The individuals are large (6.4 mm. in length) 
and fine and apparently normal in form. This species was found alive at 
St. Joseph where pollutional conditions are bad, and was also abundant 
at the stations lower down the stream where living mussels or pectinibran- 
chiate snails were very rare or absent. Ancyli were not observed in Spoon 
River, in Middle Fork, or below the dam at Homer Park. Found by Mr. 
Zetek in the Sangamon River at White Heath. 
54. Ferrissia tardus Say. River Limpet. 
This Ancylus is in the author’s collection from White Heath and 
Monticello, Sangamon River, and from the Salt Fork near Urbana, col- 
lected by Mr. Zetek and identified by Dr. Bryant Walker. No tardus 
were collected during the present survey. 
55. Gundlachia meekiana Stimpson. 
Specimens of this characteristic mollusk are in the author’s collection 
from Crystal Lake, Urbana, collected by Mr. Zetek in August 1904, and 
identified by Dr. Walker. None were seen during the present survey. 
In the catalogue of the Mollusca of Illinois (Baker, 1906: 101, 102) 
Ancylus (Ferrissia) shimekii Pilsbry is recorded from Salt Fork, Urbana, 
and Ancylus (Laevapex) kirklandi Walker from Crystal Lake, Urbana. 
These species were contained in the collection of the State Laboratory 
of Natural History. A recent examination of the material upon which 
these records are based indicates that there has been an error in the habitat 
given. None are from the Salt Fork or Crystal Lake. Ancylus kirklandz, 
identified by Walker, is in the laboratory collection from Havana, Illinois 
River (Nos. 13792, 13811, 24123) and Elizabethtown, Illinois (No. 24527). 
Ancylus shimekii (No. 24541) is in a bottle with Ancylus rivularis, both 
identified by Walker. The bottle is without locality and no record was 
found in the laboratory catalogs of the specimens bearing this number. 
It is evident, therefore, that these species of Ancylus must be eliminated 
from the list of the fauna of Salt Fork. 
( 
