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 MoUusca of Illinois (Baker, 1906: 101, 102) 

 Ancylus (Ferrissia) skimekii 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 kirklandi, 

 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. 



