182 



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, everywhere 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, broadly and 

 bluntly rounded, 2.7 to 3.3 in head; mouth very large, terminal, oblique, tip 

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

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



Fig. 26 



Left branchial cavity of Semotilus alromacidatus, with opercle removed 

 to show left pharyngeal arch in situ; also pharyngeal jaws removed 

 and viewed from front. 



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, equidistant between front 

 of eye and base of caudal; longest dorsal ray 1.6 to 1.8 in head; anal rays 

 8; pectorals short, reaching x /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, consider- 

 ably 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 an increase in its numbers is very noticeable 



