54 



Artificial Key to the Families" of Native Fishes of Illinois. 

 (Adapted from Jordan and Evermann.) 



I. Mouth circular; body elongate: no paired fins; gill-openings seven in number, not 



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

 body in the jugular region Petromyzonid^. 



II. Mouth a transverse cleft (more or less modified by form and position of tne lipsi; gill- 



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

 A. No median barbel on chin. 



1. Ventral fins present, abdominal. 



a. Tail evidently heterocercal. 



b. Body naiied, snout wide and spatulate; mouth large; teeth minute or wanting; no 



barbels Polyodon'TID.e. 



bb. Bodv with five series of bony shields; mouth inferior, toothless, preceded bv four 



barbels AciPEXSERiD.c 



bbb. Body with scales. 



c. Scales ganoid; dorsal fin short; nogular plate Lepisosteid.e. 



cc. Scales cycloid; dorsal fin long; large, bony gular plate Amiid.e. 



aa. Tail not evidently heterocerc. 



c. Head with eight long barbels; body naked. Silcrid.e. 



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 finlets. 



e. No adipose tin. 



f. Eyes normal; vent behind ventral tins. 



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 C.\TOSTO.MID.F.. 



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

 phar>'ngeal teeth fewer than eight, in one to three rows CyprTnid.e. 



gg. Gill membranes free hnm 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 H iodon'TID.e 



jj. Mouth small or moderate; no lateral line. 



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

 gate DOROSOMID.C. 



kk. Mouth terminal; maxillary in three pieces; stomach not gizzard-like. .Clupeid.e. 

 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 Ll'CilD.E. 



II. Lateral line wanting. 



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



mm. Upi)erjaw protractile, premaxillaries forming its margins PoEciLiiD.c 



ff. Eyes concealed beneath skin; vent at throat Amblyopsid.e. 



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. 



Percopsid.e. 



nn. Kins without spines; scales cycloid; many pyloric caeca Salmoxid.e. 



dd. Dorsal tin preceded by four or more free spiiies G.\sterosteid.e. 



ddd. Dors:il tin preceded by a fintet of four slender spines ATHERiN'in.E 



2. Ventral fins wholly wanting. 



a. Body much elongated; dorsal, anal, and caudal fins continuous around body. 



.AXCUILLID.E. 



aa. Body not elongate; fins separate; eyes imperfect Ambly"OPSID.f. . 



.3. Ventrals thoracic or jugular, the number of rays not I, ."), but usually 1, 7; dorsal with 



three or four spines; scales strongly ctenoid Aphredoderid-E. 



4. Ventral tins thoracic or subjugular; the number of rays definitely I, 5; dorsal with 



spiny and soft rays; slit belnnd fourth gill large; body scaled. 



a. Lateral line never extending on rays of caudal fin; often incomplete or wanting. 



b. Pseudobranchia undeveloped. 



c. Anal spines 3 to 10. 



d. Dorsal s|)ines 4; lateral line wanting El..\ssOMlD.E. 



dd. Dorsal spines (i to 12; lateral line well developed Cextrarchid.c. 



cc. .\nal spines 1 or 2; small fishes under eight inches long Percid.e, 



bb. I'seuilobranchia developed. 



e. Anal spines 2 ^or 1); pseudobranchia small; cylindrical fishes Percid.e. 



