FISHES OF THE MISSOURI RIVER BASIN. 381 



Micropterus has not been found west of Ravenna, Nebr. (98° 30' W.), and 

 it is not likely that it occurs naturally even that far west. 



Of the four darters whose range extends farthest west in this basin, 

 Boleosoma nigrum reaches only to Dakota River, Hadropterus aspro to 

 Ewing, Xebr. (98° 20' W.), and to Jamestown, N. Dak. (98° 30' W.). 

 Etheostoma iowas extends still farther west, it having been found by us 

 at Valentine, Nebr. (100° 30' W.), while Boleichthys eocilis, a somewhat 

 doubtful species, was found by Dr. Suckley even a little farther west 

 in North Dakota. 



THE ICHTHYOLOGIC PECULIARITIES OF THE BLACK HILLS. 



The fish fauna of that portion of the Missouri system lying in and 

 about the Black Dills is peculiarly restricted in its character, and 

 presents a number of interesting problems in geographic distribution. 

 The physical conditions of the region are briefly these: 



(1) An isolated, mountainous region, approximately 75 by 100 miles 

 in extent, covered with heavy pine forests and drained by more than a 

 dozen good-sized creeks, whose waters are naturally cold, clear, and 

 pure, and all flowing east, northeast, or southeast to the north or south 

 fork of the Cheyenne. 



(2) Surrounding this region on all sides is a broad plain 100 to 200 

 miles wide, in which the soil is full of alkali, where the rainfall is not 

 great, where there are no forests, and where even herbaceous vegeta- 

 tion is very scant, where the soil is eroded with great ease, the streams 

 are shallow, their beds constantly shifting, the water warm in the 

 summer time and always strongly alkaline and full of solid matter in 

 suspension. To the east and northeast, country of this character extends 

 from the base of the Hills to the Missouri River at least, a distance of 

 not less than 150 to 200 miles. To the southward is a broad strip almost 

 equally uninviting, while on the west, extending from the base of the 

 Hills to the Powder River, the country is barren in the main and the 

 streams are of the same general character. Among the low hills on 

 the east of the Powder River Valley are the headwaters of two streams; 

 one of these is the Belle Fourche or north fork of the Cheyenne, which 

 flows to the northeast and sweeps around the north base of the Black 

 Hills; the other is the south fork of the Cheyenne, which, flowing east 

 and south, hugs the south base of the Hills a little less closely, and 

 then turning northeast unites with the north fork 30 or 40 miles east 

 of the Hills, thereby forming the Big Cheyenne, which, after a course 

 of more than 100 miles in a northeasterly direction, flows into the Mis- 

 souri. Into one or the other of these two forks flow all the streams of 

 the Hills. 



Most of these streams were examined by us and collections made from 

 them at many different places. Only 15 species of fishes were secured, 

 and no other species has ever been reported from any definite locality 

 of this region. The 15 species known from the Black Hills represent 



