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 skm is dark brown, relieved by two lig'hter 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 (i 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. 1 
The Feather-Backs,— Family Notoeteridje. 
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 Physostomi, of which, in the 
scheme here followed, it should be only a section. 
