56 



HIGH SCHOOL ZOOLOGY. 



structurally far more diverse than is the case iu other Families 

 of Fishes. All of its members possess the barbels, the well 

 developed premaxillaries, aud the rudimentary maxillary bones 

 of the Catfish, they lack the sub-operculum, but they all have 

 the curiously modified anterior vertebrae and air-bladder, although 

 sometimes these are difficult to detect. They are for the most 

 pai-t fresh-water forms, but a few are marine. 



As we have studied a representative of this group in detail, 

 some account of its most striking tropical forms may be of 

 interest. 



Reference has been only made to the fresh-water catfishes above ; there 

 are, however, representatives of the family on the sea coast extending 

 from Cape Cod southwards. These belong to two genera, Arius and 

 ^luriclitliys, which agree in having the head armed above with Ijony 

 shields; in this respect they are less like our catlish than the large cat- 

 fish of the Nile ( Bagrus) and of the South American rivers ( Pimelodus) 

 are, and they more nearly approach certain other South American forms — 

 Doras and its allies, where the head is completely mailed, but where the 

 branchial aperture is reduced to a mere slit so that water can be retained 

 in the gill-cavity. This latter condition also occurs in the Electric Cat- 

 fish of the Nile ( Malapterurus, Fig. 21) which has no exoskeleton, but 

 has the superficial layer of muscles converted into an electric organ. 



Fig. 21.— Electric Catfish of the Xile. M Inptcniras eledricus. ■^. 

 (After Brehm). 



