Artificial Key to the Families op Native Fishes of Illinois. 

 (Adapted from Jordan and Evermann.) 



I. Mouth circular; body elonsrate; no paired fins; grill-openings geren in number, not 



covered by an operculum, but opening externally as large pores on the side of the 

 body in the jugular region Fetromtzonid^. 



II. Mouth a transverse cleft (more or less modified by form and position of the lips): Bill- 



openings covered by an operculum; one or two pairs of fins, not median. 



A. No median barbel on chin. 

 1. Ventral flns present, abdominal. 



a. Tail evidently heterocercal. 



b. Body naked, snout wide and spatulate; month large; teeth minute or wanting: 



no barbels Poltodontid^. 



bb. Body with five series of bony shields; mouth inferior, toothless, preceded 

 by four barbels Acipkkseeid^. 



bbb. Body with scales. 



c. Scales ganoid; dorsal fin short; no galar plate Lspisosteid^. 



cc. Scales cycloid; dorsal fin long; large bony gular plate Amiidje. 



aa. Tail not evidently heterocercal. 



c. Head with eight long barbels; body naked Silurid.*:. 



cc. Head without elongate barbels (except, in some instances, at comers of mouth) : 

 body more or less completely scaled. 



d. A single dorsal fin, not preceded by free spines or detached flnlets. 



e. No adipose fin. 



f. Eyes normal; vent behind ventral flns. 



g. Gill membranes broadly joined to isthmus; fins all soft; no teeth in jaws. 



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

 covered with plicate or papillose skin; pharyngeal teeth numerous and comb- 

 like Catostom ID^. 



hh. Dorsal fin of not more than ten rays; lips usually thin, never plicate, or papil- 

 lose; pharyngeal teeth fewer than eight, in one to three rows Ctprinidae. 



gg. Gill membranes free from Isthmus; dorsal and anal fins situated well back 

 on body. 



i. Head naked; belly narrow and carinated; silvery fishes. 



j. Mouth large; lateral line present Hiodontid.s. 



jj. Mouth small or moderate; no lateral line. 



k. Mouth inferior, small; stomach gizzard-like; last rays of dorsal much elongate. 



DOROSOMID.^:. 



kk. Mouth terminal; maxillary In three pieces; stomach not glzzard-Uke. 



CLUPEID.S. 



ii. Head more or less scaly; anal fin short. 



I. Lateral line present, somewhat irregular; scales small; teeth" on maxillaries, 



etc., cardiform; jaws depressed, duck-bill like Luchd^. 



II. Lateral line wanting. 



m. Upper jaw not protractile; teeth villiform Umbrid.s. 



mm. Upper jaw protractile, premaxillarles forming its margin Pobcihid.e. 



ff. Eyes concealed beneath skin; vent at throat Ambltopsid^. 



ee. An adipose fin behind a dorsal fin composed of rays and a spine. 



n. Dorsal, anal, and ventral fins with small but distinct spine; scales ctenoid. 



Pbrcopsida. 



