172 FISHES OF ILLINOIS 



Order NEMATOGNATHI 



(the catfishes) 



Skeleton bony; four anterior vertebrae coossified, modified, and fur- 

 nished with a chain of small bones (Weberian ossicles) connecting the air- 

 bladder (if present) with the auditory organ ; ventral fins abdominal ; dor- 

 sal and pectorals each with a single spine; pectoral arch suspended from 

 the skull; a mesocoracoid arch present; suboperculum wanting, or modi- 

 fied into the uppermost branchiostegal; premaxillary forming border of 

 mouth (except in the genus Diplomystes, of Chili), the maxillary being 

 often rudimentary and supporting the base of a barbel; air-bladder, if 

 present, with open duct (physostomous). A large group, comprising 

 some 1,200 species and ISO genera, found in the fresh waters of both 

 hemispheres and of all the continents, few species being marine; most 

 abundant in the Amazon region. Most species are naked-skinned, 

 although the numerous small forms of the South American family Lori- 

 cariidce* have the sides and back armored with rough bony plates. 



Family SILURID.E 



(the catfishes) 



Body more or less elongate, naked or covered (in many South Ameri- 

 can forms) with bony plates; no true scales; lateral line usually present; 

 skeleton osseous; 4 anterior vertebra? modified, and furnished (in forms in 

 which air-bladder is developed) with a chain of small bones (Weberian 

 ossicles) connecting the air-bladder with the ear; -ventral fins abdominal; 

 anterior rays of dorsal and pectorals usually spinous; an adipose fin 

 usually present; tail not heterocercal ; mesocoracoid present; gill-openings 

 generally wide; suboperculum wanting, or modified into the uppermost 

 branchiostegal; margin of upper jaw formed by premaxillaries only; 

 teeth in jaws in broad bands; lower pharyngeals separate; air-bladder 

 usually present, simple, with open duct, connected (see above) with the 

 organ of hearing by Weberian ossicles. 



'Phis family is very large and widely distributed, embracing 

 about 700 species, found chiefly in fresh water, in all parts of the 

 globe. Catfishes are most abundant in tropical and subtropical 

 regions. Some species grow to a very large size, and all except the 



*Some tropical SiluridcB arc imperfectly mailed. 



