2 FISHES OF ILLINOIS 



II. An adipose fin Salmonidse. Page 60. 



kk. Gill -membranes more or less broadly joined* 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 cov- 

 ered 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 papil- 

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



Cyprinidae. Page 94. 



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

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

 chin barbels in fresh-water forms of United States) .. .Siluridaa. 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). 



. . Pceciliidae. Page 210. 



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



more or less concealed beneath skin; ventrals ordinarily wanting 



'. . Am blyopsidae. 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 flnlet 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 - Percopsidae. Page 225. 



ss. Dorsal fin preceded by a finlet of 3 to 8 slender spines. . Atherinidas. Page 226. 

 bb. Ventral fins thoracict or jugular. 



u. Ventral rays usually I, 7 (I, 6 or 7) ; vent in front of pectorals 



Aphredoderidae. Page 228. 



uu. Ventral rays I, 3 to I, 5, typically I, 5; vent normal. 

 v. Chin without barbel. 

 w. Body scaled. 

 x. Anal spines 3 to 10. 



y. Lateral line wanting Elassomidae. Page 231. 



yy. Lateral line present. 



z. Dorsal fins confluent, the spinous portion always somewhat lower than the 

 soft portion; in forms with deep notch between dorsal fins, the highest 

 dorsal spine but little more than half the height of the highest soft ray. 



Centrarchidae. Page 232. 



zz. Dorsal fins either (1) separate, and the soft and spinous portions about 

 equally high; or (2) barely confluent, with the notch between them very 

 deep and with the highest dorsal spine as high as, or higher than, the 

 highest soft ray (marine forms not included) Serranidae. Page 318. 



* 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 dis- 

 tance from the same point to the back of the orbit. 



f 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 Cen- 

 trarchidce; in which, however, the ventrals are nearer to the throat than to the first soft ray of 

 the anal. 



