120 



LOWER VERTEBRATES. 



at Key West. The animal gave a vigorous shock, to the surprise of its captor, who 

 was uuacquainted with its electric powers. 



The NeiiiatogenyinsB comprise about three species of small fishes from South 

 America. Tliese have the dorsal above the ventrals, and ajJi)roach in many respects 

 the next family, with which they are associated by Dr. Giinther. 



The family Tbichojiycterid.*: is distinguished from the Siluridoe by the position 

 of the dorsal tin, which is inserted behind the ventrals, the latter fins being sometimes 

 absent. About fifteen species are known ; small fishes inhabiting the Andean regions 

 in South America, some of them at great altitudes. Some of them (sub-family Stego- 

 philinie) are very small fishes which live in tlie gill cavities of larger Siluroids. Tliey 



are probably not j)arasites, but enter these cavities for protection merely. The resem- 

 l)lance of the fishes of this family to the Cobitid», or loaches, lias been noticed by Dr. 

 .Giinther. Their likeness in aj)pearance and habits, and even in coloration, offers " a 

 striking example of the fact that similar forms of animals are j)roduced under similar 

 external physical conditions." 



■ The family of Hypopiithalmid.e diverges from the other Nematognathi, as already 

 stated, in the unmodified character of the anterior vertebrae. The lower jiharyngeal 

 bones are finnly united, and the number of branchiostegals much increased. The gill 

 openings are very wide, and the gill arches are armed with long gill rakers. The 

 dorsal fin is behind the ventrals, and the adipose fin is very small. There are six 

 barbels. The skin is everywhere smooth. The physiognomy is peculiar from the 



