122 



FISHES OF ILLINOIS 



Length usually 6 to 8 inches, sometimes reaching a length of a foot; 

 body rather elongate, but robust, heavy forward, the back gently arched 

 in front of the dorsal fin; depth 4.1 to 4.6 in length; caudal peduncle 

 shorter than head, its depth 2 to 2 . 5 in its length. Color dusky bluish- 

 olive above; tinges of light purplish on sides as far down as lateral line; 

 a faint plumbeous lateral band, somewhat more distinct towards end of 

 caudal peduncle; a faint vertebral streak and a dark bar behind opercle; 

 sides below lateral line greenish gray to silvery- ; belly silvery ; dorsal fin 

 with a distinct black blotch at base, between first and third rays; in 

 breeding males there is sometimes a broad but indistinct transverse 

 bar of dusky color crossing the fin about midway; other fins plain, or, at 

 most, with slight traces of dusky in spring males. Head large, every- 

 where convex, broadly rounded above, 3.5 to 3.9 in length; width of 

 head 1 . 6 to 1 , 8 in its length ; interorbital space 2 . 4 to 2 . 7 ; eye 4 . 8 to 7 . 1 

 in head, usually more than 6 in adults; nose long, broadlv and bluntly 

 rounded, 2.7 to 3.3 in head; mouth ver}- large, terminal, oblique, tip of 

 upper lip at level of lower margin of pupil; maxillary about 2^ times eye, 



Fig. 26 

 Left branchial cavity of Semotiliis atroinaculatus, with opercle 

 removed to show left pharyngeal arch in situ ; also pharyn- 

 geal jaws removed and viewed from front. 



reaching beyond anterior margin of orbit; jaws about equal; isthmus 

 less than eye. Teeth extremely variable, — 4,1-0,4, 4,1-0,5, 4,2-1,5, 

 4,2-2,5, 5,2-1,5,4,2-2,4 in nine specimens examined by us; intestine 

 . 9 to 1.1 times length of head and body ; peritoneum pale, a very little 

 dusky forward. Dorsal fin with 8 rays, situated behind ventrals, equi- 

 distant between front of eye and base of caudal; longest dorsal ray 1 .6 

 to 1 . 8 in head; anal rays 8; pectorals short, reaching i to § to ventrals, 

 1.5 to 1.9 in head; ventrals short of vent in adults. Scales 10 or 11, 

 rarely 9, 55 to 69, 5 to 7, considerably crowded in predorsal and scapular 

 regions, about 35 rows before dorsal fin; lateral line complete, with a 

 strong downward curve in front of ventrals. 



This is essentially a creek species, our frequency coefficient for 

 creeks being 3.77, and for the smaller rivers 1.67. In lakes and 

 ponds we have taken it but 5 times in 591 collections, and in the 

 larger rivers but 5 times in 293 collections. Its preference for creeks 

 is also reported by R. C. Osburn, who says that in seining up stream 



