2 FISHES OF ILLINOIS 



k. Gill-membranes "free"* from isthmus, i. e., split far forward and meeting 



in an acute angle. (Fig. 8.) 

 1. No adipose fin; belly narrow, carinated; silvery fishes. 



m. Lateral line present Hiodontidae. Page 42. 



mm. Lateral line wanting. 



n. Last rays of dorsal fin much elongated; mouth small, low 



Dorosomidae. Page 45. 



nn. Dorsal fin normal, its last rays not elongated; mouth large, terminal, 



oblique Clupeidae. Page 47. 



11. An adipose fin Salmonidae. Page SO. 



kk. Gill-membranes more or less broadly joinedf to isthmus, not meeting in 

 an acute angle. (Fig. 9.) 



o. Ventral fins wanting; body eel-shaped Anguillidae. Page 58. 



oo. Ventral fins present; body not eel-shaped. 

 p. Dorsal fin of more than 25 rays, or shorter, and the lips thickened 

 and covered with plicate or papillose skin; pharyngeal teeth numerous 



and comb-like Catostomidae. Page 61. 



pp. Dorsal fin of not more than 10 rays; lips usually thin, never plicate 



or papillose; pharyngeal teeth fewer than 8 on a side, in 1 to 3 rows 



CyprinidaB. Page 94. 



jj. Body and head naked (except in some tropical forms); head typically 

 furnished with 4 to 8 long barbels (1 pair nasal, 1 pair maxillary, and 2 



pairs chin barbels in fresh-water forms of United States) 



Siluridas. Page 172. 



ii. Head scaly; body completely scaled. 



q. Lateral line present; jaws shaped like a duck's bill . . . . Esocidae. Page 205. 

 qq. Lateral line wanting. 



r. Upper jaw not protractile Umbridae. Page 202. 



rr. Upper jaw protractile (i. e., the upper lip separated from the skin of the 

 forehead by an evident groove, which passes wholly across the muzzle). 



Poeciliidae. Page 210. 



hh. Vent jugular, in front of pectorals and close behind gill-openings; eyes 



more or less concealed beneath skin; ventrals ordinarily wanting 



Amblyopsidae. Page 217. 



gg. Dorsal fin with either (1) a single spine (occasionally 2), in which case the 

 ventrals are inserted distinctly nearer to the first ray of the pectorals than 

 to the first ray of the anal and an adipose fin is present ; or (2) with two or 

 more free spines; or (3) preceded by a separate spinous dorsal finlet of 4 

 or more spines. 

 s. Dorsal with a single spine or preceded by 4 or more free spines. 



t. No adipose fin; dorsal free, preceded by 4 or more free spines 



Gasterosteidae. Page 221. 



tt. An adipose fin; dorsal, anal, and ventral fins each with a weak and rather 



indistinct spine Percopsidas. Page 225. 



ss. Dorsal fin preceded by a finlet of 3 to S slender spines. . Atherinidae. Page 226. 

 bb. Ventral fins thoracicj or jugular. 



* See note under kk. 



t In these forms the distance from the tip of the snout to the angle of the gill- 

 membranes or to a transverse line connecting the lower corners of the gill- 

 openings is greater than the distance from the same point to the back of the orbit. 



t In all Illinois species of the following families (below bb) the ventrals are 

 distinctly nearer to the throat (angle of gill-membranes), or to a transverse line 

 connecting the lower corners of the opercular openings, than to the first anal 

 spine, except in the deep-bodied genera of Centrarchidce; in which, however, 

 the ventrals are nearer to the throat than to the first soft ray of the anal. 



