SILURIDJB. CX. 327 



between the intermaxillaries and the eyes; the anterior 

 are suboval or subcircular, and the posterior linear, with 

 a raised margin, from the front of which the upper bar- 

 bels originate; the eyes are generally placed in the 

 anterior half of the head; the dorsal and pectoral fins 

 are each provided with a stout, pungent spine. The adi- 

 pose fin is developed, not rayed, and the rays of the 

 dorsal fin are few in number. The branchial apertures 

 are ample, continued from the supero-posterior angles 

 of the opercula to beneath the throat. The air-bladder 

 is well developed. The species commonly inhabit deep 

 or sluggish waters, and are very tenacious of life 

 especially those of Amiurus. 

 * Adipose fin with its posterior margin free, not connected with 



the caudal fin. 



f Intermaxillary band of teeth convex in front, abruptly trun- 

 cate behind, without lateral backward processes ; branchi- 

 ostegals 8 or 9 (rarely 10 or 11) ; ventral fins normally with 

 8 rays. 



\ Supraoccipital bone prolonged backward, its apex emar- 



ginate, receiving the pointed anterior end of the second 



interspinal, thus forming a continuous bony bridge from 



the snout to the base of the dorsal ; branchiostegals 8 or 



9; head elongate; mouth small, terminal, the upper jaw 



the longer; anal fin elqngate, of 34 to 34 rays; caudal 



fin furcate ; body elongate, more or less slender, silvery, 



covered with thin skin. . . ICHTH^LURUS, 1. 



\\ Supraoccipital bone free behind, not connected with 



the interspinal ; branchiostegals normally 9 (varying 



from 8 to 11) ; head broad ; mouth broad, terminal ; 



anal fin moderate or rather long, with 15 to 27 rays ; 



caudal fin usually truncate, but often more or less 



deeply emarginate or even forked; body usually 



more or less shortened, covered with a rather thick 



skin AMiURtis, 2. 



ff Intermaxillary band of teeth convex in front, with a lateral 

 backward extension on each side; branchiostegals nor- 



