618 FISHES. 



heUerii), besides, the lower caudal rays of the mature male 

 aj? e prolonged into a long, sword-shaped, generally black and 

 yellow appendage. 



Two other genera belong to this group : Platypoecilus and 

 Girardinus. 



Seventh Family — Heteeoptgii. 



Head naked ; hody covered with very small scales ; harlels 

 none. Margin of the upper jaw formed hy the intermaxillaries. 

 Villiform, teeth in the jaws and on the palate. Adipose Jin 

 none. Dorsal fin helonging to the caudal portion of the vertebral 

 column, opposite to the anal. Ventral fins rudimentary or 

 absent. Vent situated before the pectorals. Stomach coecal ; 

 pyloric appendages present. Pseudolranchia; none ; air-bladder 

 deeply notched anteriorly. 



To this small family, which is closely allied to the 

 Cyprinodonts and Umbridse, belongs the famous Blind Pish 

 of the Mammoth Cave in Kentucky, AmUyopsis spelmus. It 

 is destitute of external eyes, and the body is colourless; 

 although the eyes, with the optic nerve, are quite rudimentary, 

 the optic lobes are as much developed as in fishes with per- 

 fect eyes. The loss of vision is compensated by the acute- 

 ness of its sense of hearing, as well as by a great number of 

 tactile papilljB, arranged on transverse ridges on the head, and 

 provided with nervous filaments coming from the fifth pair. 

 The ovary is single, and the fish is viviparous, like the 

 Cyprinodonts. It seems to occur in all the subterranean 

 rivers that flow through the great limestone region under- 

 lying the carboniferous rocks in the central portion of the 

 United States. As in Gyprinodon, so in this genus, specimens 

 occur without ventral fins ; they have been called Typhlich- 

 thys. The largest size to which AmUyopsis grows is five 

 inches. 



Ghologaster is closely allied, but provided with small 



