326 FISHES. 



ORDER AA. JSTEMATOGNATHI. 



(The Shcat Fishes.\ 



Skin naked or with bony plates; no true scales; bar- 

 bels always present, maxillary bone rudimentary and 

 forming the base of the longest barbel; margin of upper 

 jaw formed by intermaxillaries only; sub-opercle absent; 

 air bladder generally present; usually an adipose fin, 

 and in all our species a spine in the dorsal and pectorals; 

 ventrals abdominal. Chiefly fresh water fishes, inhabit- 

 ing most regions, especially abounding in South America. 

 The leading family is SiluridcB. 



FAMILY CX.-SILURID^E. 



(The Oat Fishes.) 



General characters as above given; genera one hund- 

 red or more; species nearly seven hundred; a very large 

 family abounding in the fresh waters of America and 

 the warmer parts of the Old World; a few are marine. 

 Our species constitute a peculiar group termed by Dr. 

 Gill Ichthceluri. The characters of this group are as 

 follows : The body is more or less elongated, compressed 

 posteriorly, and terminating in a well-developed caudal 

 fin. The skin is naked and unprovided with sucking 

 cups; the head in profile presents the appearance of a 

 more or less elongated cone, and is covered with a skin 

 which is generally quite thick; it is more or less flat- 

 tened, and broad above, and gradually becomes narrowed 

 to the convex snout; there is never a casque, or helmet; 

 the supraoccipital terminates in a point; there are eight 

 barbels: the two maxillary, constant in the family; a 

 pair in front of the posterior nasal apertures; and two 

 pairs arranged in a curved line behind the lower jaw; 

 the nostrils form nearly a transverse parallelogram 



