Jordan and Evcrmann. — Fishes of North America. 115 



aa. Air bladder rudiineutary, one divisiou oa either side of the coalesced vertebraj aud entirely 

 surrounded by a bony capsule; this capsule, formed by the skull and by the lat- 

 eral processes of the anterior vertebra"; diaphragm wholly ussciius, formed liy the 

 expansions of the clavicle and scapular process. Scapula and its prucess firmly joined 

 to the skull. Gill niombranea joined to the isthmus; skin covered with bony plates. 

 6. Caudal vertebra; compressed, the neural and haemal spines expanded, forming a con- 

 tinuous ridge above and below; skin with several series of plates; mouth inferior, 

 the lower lip reverted; teeth turned abruptly back above and usually expand<-d; 

 a single series of teeth erect and in function, the premaxillarics and dcniaries box- 

 shaped, filled with numerous relay teeth; intestinal canal coiled; cavity of air 

 bladder communicating with the exterior at a notch in the posterior margin ol the 

 temporal plate at beginning of lateral Hue. Lobicauiid.k, xxx v. 



Family XXXIV. SILURID^. 



(The Catfishes.) 



Body more or less elongate, naked or covered with bony plates. No 

 true scales. Anterior part of bead with 2 or more barbels, the base of 

 the longest pair formed by the small or rudimentary ma.villary. Margin 

 of upper jaw formed by premaxillaries oulj'. Suboperculum absent; 

 operculum present. Dorsal fin usually present, short, above or in front 

 of the ventrals. An adipose tin usually present. Anterior rays of dorsal 

 and pectorals usually spinous. Air bladder usually present, large, and 

 connected with the organ of hearing by means of the auditory ossicles. 

 Lower pharyngeals separate. 



After the removal of numerous aberrant forms as distinct families, the 

 family of Silukid.k contains more than 100 genera and upward of 900 

 species. Most of the Silurid.e are fresh-water fishes, inhabiting the 

 rivers of warm regions, particularly South America and Africa; compar- 

 atively few of them are marine, and these few are mostly tropical. They 

 are especially characteristic of the Amazon region in South America. 

 (SiLURiDiE, part, Giznther, Cat., v, 30-65; 69-220.) 



a. Gill membranes free or forming a free fold across the isthmus, rarely joined to the isthmus; 

 anal fin shorter than caudal jjortion of vertebral column. 

 Tachysuein-e: 



h. Nostrils close together, neither with a barbel, the posterior with a valve; teeth mi the 

 palate; caudal forked. (Species chiefly marine.) 

 c. Lower jaw with 2 barbels; maxillary barbel band-like; pectoral s|)iiie with a band- 

 like filament. FKLiciiTiivt;, G8. 

 cc. Lower jaw with 4 barbels; palatine teeth fixed; both jaws with teeth, 

 d. Gill rakers few, 5 to 25; eyes above level of mouth. 



Galf.ichthvs, etc., (genera CD to 74). 

 dil. Gill rakers very many — 40 or more, long and slender; eyes scarcely above 

 level of mouth. Cathokops, 7r>. 



hh. Nostrils remote from each other. (Fresh- water species.) 



ICTALURINJE: 

 e. Posterior nostril with a barbel; barbels 8; no teeth on vomer or palati^. 

 /. Adipose fin with its posterior margin free. 



</. I'remaxillary band uf teeth truncate behind; not iirodiued backward at 

 the outer angles. 

 h. Eyes normal. 



