Order in. Nematognathi. 



The Catfishes. 



Fishes with the four anterior vertebrae co-ossified, and with ossicula 

 auditus; maxillary rudimentary, forming the base of a conspicuous 

 barbel; no subopercle; body naked, or more or less covered with 

 bony plates. A large order comprising several families, only one 

 of which is represented in Mexico. 



Family III. Siluridse. 



Body more or less elongate, naked or covered with bony plates; 

 no true scales; anterior portion of the head with two or more barbels, 

 the base of the longest pair formed by the small or rudimentary 

 maxillary; margin of the upper jaw formed by the premaxillaries 

 only; subopercle absent; opercle present; dorsal fin usually short, 

 opposite to or in front of ventrals; adipose fin present; anterior 

 rays of dorsal and pectoral fins spinous; air bladder usually present, 

 large, and connected. with the organ of hearing by means of auditory 

 ossicles; lower pharyngeals separate. 



The catfishes of Mexico allied to those found in the United States, 

 have representatives known as far south as the Rio Usumacinta in 

 Guatemala. None of the South American forms have yet been 

 taken farther north than Cordoba and Orizaba. 



KEY TO THE GENERA OF SILURID/E. 

 a. Adipose fin small, its posterior margin free. page 



b. Nostrils close together, neither with a barbel, 



the posterior with a valve; teeth on palate . . . .Galeichthys 9 

 bb. Nostrils remote from each other, 

 c. Posterior nostril with a barbel; barbels 8, the 

 longest reaching past eye ; teeth on the lower 

 jaw well developed, 

 d. Premaxillary band of teeth truncate behind, 

 not produced backward at the outer angles, 

 e. Supraoccipital bone continued backward 

 from the nape, its notched tip receiving the 

 bone at base of dorsal spine, so that a con- 

 tinuous bony bridge is formed under the 



skin from snout to base of dorsal Ichihycelurus ro 



ee. Supraoccipital bone not reaching inter- 

 spinal bones; the bridge incomplete Amiurus 12 



8 



