618 FISHES. 



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

 are prolonged into a long, sword-shaped, generally black and 

 yellow . appendage. 



Two other genera belong to this group : Platypoecilus and 

 Girardinus. 



Seventh Family — Heteropygii. 



Head naked ; hody covered with very small scales ; harhels 

 none. Margin of the upper jaio formed hy the intermaxillaries, 

 Villiforni teeth in the jaws and on the -palate. Adipose fin 

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

 column, opposite to the ancd. Ventral fins rudimentary or 

 absent. Vent situated before the pectorals. Stomach coeeal ; 

 pyloric appendages present. Pscudohranchicc none ; air-bladder 

 deeply notched anteriorly. 



To this small family, which is closely allied to the 

 Cyprinodonts and Umbridte, belongs the famous Blind Fish 

 of the Mammoth Cave in Kentucky, Amhlyopsis spelceus. 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 m 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 papillffi, 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 Cyprinodon, so in this genus, specimens 

 occur without ventral fins ; they have been called Typhlich- 

 thys. The largest size to which Amblyopsis grows is five 

 inches. 



Chologaster is closely allied, but provided with small 



