+ 
biologists for a considerable number of Illinois collections 
of darters. 
The drawings of P. phoxocephala and genital papillae 
were done by Mrs. Alice Ann Prickett, University of 
Illinois School of Life Sciences Artist. Assistance in pre- 
paring the illustrations was provided by Illinois Natural 
History Survey Technical Illustrator Richard M. Sheets 
and Survey Photographer Wilmer D. Zehr. ‘The manu- 
script was edited by Robert M. Zewadski, Associate 
Technical Editor of the Survey. Dr. David A. Etnier, 
University of Tennessee, served as special guest reviewer. 
THE STUDY AREA 
The area selected for study (the shaded oval in the 
lower-right quarter of Illinois in Fig. 1) extends from a 
eravel bar in the middle Embarras River //2 mile north 
of Greenup, Cumberland County, south to a site 3 miles 
west of Rose Hill, Jasper County, Il., although most 
of the collections were made over gravel bars at Greenup. 
The Embarras River, a tributary of the Wabash 
River, flows through the Wisconsinan end moraines in 
the vicinity of Charleston and has deposited large quanti- 
ties of glacial gravel and sand for the entire length of 
the study area. The water is well oxygenated by flowing 
over the many fast riffles bordering sand and gravel bars 
that alternate with deep, relatively quiet pools. Chemical 
measurements taken in the Embarras River at Camargo 
in Douglas County from October 1966 to April 1968 by 
the Illinois State Water Survey and made available 
through the courtesy of Mr. Harman F. Smith, indicated 
that water quality was unusually high and that pollution 
was minimal (Page & Smith 1970:5). 
In the vicinity of the study area the stream could be 
classed as a small to medium-sized river. During low 
water stages the channel was only 15—30 feet wide and 
in riffle areas barely a foot in depth, although there 
were some deep pools at bridge sites and at abrupt bends 
in the river. During flood stages the inundated flood- 
plain was almost 1 mile wide. 
One of the principal study sites, 1 mile west of 
Greenup, had a variety of habitats, consisting of gravel 
bars and gravelly raceways, sandbars and sandy race- 
ways, a rubble riffle, and several silt-bottomed pools. 
Fig. 2.—Study area on the Embarras River ¥2 mile north of Greenup, III. 
