FEA THER-BA CKS. 



475 



the dorsal fin is relatively short, scarcely exceeding the anal in length, while the 

 muzzle is long and bent down. From its nearest allies the species in question is 

 distinguished by the production of the extremity of the lower jaw into an 

 elongated, conical, dependent, fleshy appendage, nearly equal in length to half 

 the head. In colour the skin is dark brown, relieved by two lighter crossbands 

 between the dorsal and anal fins. Other species have the muzzle short and blunt ; 

 and whereas some grow to a length of between 3 and 4 feet, others are compara- 

 tively small fishes. No less than eleven species of this genus are found in the 

 Nile ; which, together with some of the West African rivers, is likewise the home 

 of the single representative of the genus Gymnarchus. In form the latter fish 



PETERS' BEAKED FISH AND SLENDER PIKELET (^ nat. size). 



is eel-like ; its jaws being armed with a series of incisor-like teeth, and its length 

 reaching to upwards of 6 feet. Both genera are furnished with a pair of organs 

 lying on the two sides of the tail, which are stated to be transitional in 

 character between ordinary muscle and a true electric organ ; although, if this be 

 correct, it is difficult to conceive what can be the object or use of such a structure. 

 Each consists of an oblong capsule, divided by vertical partitions into a number of 

 chambers filled with a gelatinous substance. One of the species (M. oxyrhynchus) 

 from the Nile, is frequently depicted in the frescoes of the ancient Egyptians. 



SECTION ISOSPONDYLI.i 

 THE FEATHER-BACKS, Family NOTOPTEEID^E. 



According to the classification we are following, the whole of the remaining 

 members of the tube-bladdered fishes form a group denominated Isospondyli, and 



1 On p. 333 the group Isospondyli is given as of equivalent rank with the Physostonii, of which, in the 

 scheme here followed, it should be only a section. 



