MOXOSTOMA — RED-HORSE 91 



This species, much the most abundant of the Illinois red- 

 horse, occurs outside our limits from the St. Lawrence and the 

 Hudson rivers through the Great Lakes to the Missouri River, 

 north to Winnipeg and the Assiniboin, and southward to 

 Arkansas and Georgia. In this state it is much the commonest 

 in the northern and eastern two-thirds of our area, showing a 

 tendency, like the preceding species, to avoid the turbid waters 

 of southern Illinois, although present in the clearer waters ' 

 south of the lower Illinoisan glaciation. It occurs in 148 of our 

 collections, most abundantly, in proportion to the number 

 made, in the Rock River and the northwest basins, and in the 

 Kaskaskia and Wabash systems. It has been taken by us, 

 however, in all the other stream systems except that of the Big- 

 Muddy. It is much the commonest in creeks and the smaller 

 rivers, the numbers found in the larger rivers being only half the 

 normal ratio for the species, and those in lakes and sloughs a 

 fourth that ratio. Its preference for swiftly flowing streams and 

 its avoidance of a mud bottom are also conspicuously shown 

 by our data of ecological distribution. 



This red-horse is not tenacious of life, but dies quickly in 

 the aquarium if the water is in the least impure. It also readily 

 succumbs to impure conditions of its native waters such as are 

 likely to occur in midsummer, sometimes perishing in vast num- 

 bers and stranding along the banks when violent summer rains, 

 following long periods of drought, overload the streams with 

 mud and decomposing vegetation. 



It spawns in April and May, ascending the smaller streams 

 for the purpose. Females taken from the Illinois River at 

 Meredosia May 5, 1899, were already spent. 



MOXOSTOMA BREVICEPS (Cope) 



SHORT-HEADED RED-HORSE 

 (Pl., p. 92; Map XXII) 



Cope, 1870, P. Am. Phil. Soc, 478 (Ptychostomus). 



J. & G., 141 (anisurum and (?) aureolum); M. V., 48 (crassilabre) ; J. & E., I, 196; 



N., 49 (Teretulus aureolum); J., 63 (Myxostoma aureolum); F., 80 (aureolum); 



P. P., II. 7, 444 (aureolum); L., 12 (macrolepidotum). 



Body subfusiform, moderately compressed, rather deep under front of 

 dorsal, in form much like a Coregonus; depth 3.8 to 4.4 in length. Size 

 moderate, our largest specimens about 15 inches in length. Color pale 

 yellowish olive, with a faint coppery tint on sides in predorsal region; rest of 

 sides and caudal peduncle very light pea-green, grading to whitish or dull 

 silvery lower down and on belly; dorsal very pale olive, scarcely dusky; 



