The molluscan fauna of the Big Vermilion river, Illinois, with special reference to its modification as the result of pollution by sewage and manufacturing wastes, with fifteen plates and eleven tables, by Frank Collins Baker.

Abstract

Explanation of Plates 105! FAUNA OF BIG VERMILION RIVER-BAKER 109] FAUNA OF BIG VERMILION RIVER-BAKER 11 ILLINOIS BIOLOGICAL MONOGRAPHS [114 Oligochaeta. These aquatic earthworms were abundant in places along the shore of Salt Fork. Sparganophilus eiseni Smith occurred in abundance in the mud on the margin of Salt Fork at Homer Park, and immature worm of this genus, as well as cocoons, were collected from near the bridge below St. Joseph to the bridge above Sidney. A single specimen of Belodrilus chloroticus (Savigny) was collected in the Salt Fork near St. Joseph. This species has not heretofore been recorded from Illinois and its occurrence at this locality adds another species of earthworm to the State list (see Smith, 1915:557). Limnodrilus was abundant in bottom sludges from the Salt Fork, from Urbana to near St. Joseph. Tubifex was also found, but not as abundantly. Hirudinea. Two species of leeches occurred in several places in Salt Fork, below St. Joseph. They were nowhere abundant. The two species are: Erpobdella punctata (Leidy) Moore and Placobdella rugosa (Verrill) Moore. CRUSTACEA Three species of crayfish (Cambarus) were determined by Professor Smith from the material collected in Salt Fork and other parts of the Big Vermilion River. The most abundant was Cambarus propinquus Girard, which was found commonly from bench mark 655 to the Big Vermilion River below Middle Fork. It is especially abundant in the latter place where an individual may be found under every piece of stone. The same species was abundant in Stony Creek and in the Salt Fork near Muncie. Cambarus blandingi acutus Girard, both young and adult, occurred in the upper parts of Salt Fork, but preferred a mud bottom rather than a rock bottom. Cambarus immunis Hagen was collected only at bench mark 655 where it was rare. It will be noted that Cambarus is first met with about two miles below St. Joseph and twelve miles from Urbana. The only ones seen here were dead. Living crayfish begin to appear in abundance about six miles below St. Joseph or sixteen miles below Urbana. Crayfish and mussels both become common or abundant at about the same time, viz., fourteen and sixteen miles below the source of sewage pollution at Urbana. This agreement in distribution indicates the close relationship between these otherwise diverse groups of animals, as regards resistence to septic conditions, neither being able to thrive under poUutional conditions of the bottom. AQUATIC INSECTS Aquatic insects are doubtless abundant during spring and early summer in the lower parts of Salt Fork and in the Big Vermilion River. A few species were collected incidentally at some of the molluscan stations. These are listed in Table I, in the order of their occurrence in the stream. 65 * New septic tanks have been installed at the Champaign sewage disposal plant on Salt Fork and a portion of the sewage is well treated before it enters the canal. ** Data for the sewage conditions, stream flow, chemical analyses, etc., of the Salt Fork are taken from an unpublished report o...