FISHES 91 



the Saskatchewan; eastward to Kansas City; common in river 

 channels. 



31. Exoglossum Rafinesque. Body moderately elongate; the two 

 sides of the lower jaw united its whole length, instead of forming a 

 broad arch, and looking like a projecting tongue; teeth i, 4-4, i: i 

 species. 



E. maxillingua (LeSueur). Cut-lip; nigger chub. Length 150 mm.; 

 head 4; depth 4.5; color olivaceous; a black bar behind the opercle; 

 rays of dorsal fin 8; anal 7; scales 8-53-5 • St. Lawrence River and Lake 

 Ontario to Virginia; locally abundant. 



Order 4. Heterognathi. — The four anterior vertebrae modified 

 and coossified, and Weberian ossicles present; fins soft-rayed; lower 

 pharyngeals not falciform; ventral fins abdominal; no pseudobranchiae : 

 2 families of tropical fishes, represented by a single species in Texas. 



Family Characinidae. — Adipose fin present; head naked; scales 

 cycloid : 300 species. 



Tetragonopterus Cuvier. Body oblong, compressed; lateral line 

 complete; premaxillary teeth in a double row: 40 species. 



T. argentatus (Baird & Girard). Head 4; depth 3; color olivaceous, 

 with a lateral silvery band and a black caudal spot; rays of dorsal fin 10; 

 anal 21 ; scales 6-38-6: southern Texas and Mexico; abundant. 



Order 5. Nematognathi. — Catfish. The four anterior vertebrae 

 modified and with Weberian ossicles; no subopercle; ventral fins 

 abdominal; fins soft rayed, except the dorsal and pectoral fins, each 

 of which has a single spine; scales wanting, the skin being naked or 

 with bony plates; the border of the mouth formed by the premaxillaries, 

 the maxillary being often rudimentary; barbels present on the maxil- 

 laries: several families, i in America. 



Family Siluridae. — Body elongate; upper jaw formed of premaxil- 

 laries alone; maxillaries rudimentary; 2 or more barbels on anterior 

 ])art of head; adipose fin present; a stout spine forms the anterior 

 ray of dorsal and pectoral fins; lower pharyngeals separate; air bladder 

 large: over 900 species and 100 genera, most of which are fresh water 

 fish living in the warmer regions of Africa and South America, especially 

 the Amazon region; a few species marine, mostly in tropical waters; 

 about 30 species in the United States, none of which are on the Pacific 

 slope except a few which have been introduced. 



Key to the Genera of Siluridae in the United States 



ai Posterior margin of adipose fin not adnate to back, 

 bi Rays of anal fin 17 to 35. 



