1922] 



S. L. Hora : Fish of Mountain Torrents. 



4 1 



acid, 



fins 



altitudes and rapid running streams. Similarly in the genus 

 Glyptothorax , two species, G. striatns and G. saisii, from the Khasi 

 and the Farasnath Hills 

 respectively, have a dif- 

 ferent form of caudal 

 peduncle from the re- 

 maining species. It is 

 long and harrow. In 

 almost all species of 

 Homtiloptera, Bhavania 

 and Balitora and in the 

 most specialized species 

 of the genus Garra the 

 caudal peduncle is simi- 

 larly modified. 



As regards the fin, 

 the chief modification 

 consists in the inequal- 

 ity of its lobes. In 

 most cases the lower 

 lobe is somewhat long- 

 er than the upper, as 

 in Balitora brucei, Bha- 

 vania australis, Glypto- 

 thorax -slrialus, Glypto- 

 sternum labiatum and 

 Garra nasutus. In Gas- 

 tromyzon bomeensis, though the caudal fin is not deeply forked, 

 the lower portion is longer and stronger than the upper. 



I was not able to follow the true significance of these modifica- 

 tions, because the movements were too rapid for detailed analysis. 



It may be pointed out in this connection that in Elasmobranch 

 fishes, where the mouth is on the under surface considerably be- 

 hind the tip of the snout, the lower lobe of the caudal fin is much 

 shorter than the upper. I hope to make further observations on 

 this point on another occasion. 



5. The mouth, its position and shape ; the jaws ; the barbels ; 

 the lips and their muscles. — The mode of life and the nature of food 

 in mountain-rapids necessitates a change in the position of the 

 mouth and the structure of the jaws. The mouth, instead of 

 being a transverse cleft at the anterior end of the fish, is 

 situated on the under surface considerably behind the tip of the 

 snout. It is usually crescentic or semicircular in outline. The 

 jaws are greatly strengthened and their edges become sharp and 

 cutting. In most cases, Oreinus for example, the jaws are covered 

 with a strong horny covering. This is due to the fact that hill- 

 stream fishes have to strip algal slime from stones for their food. 



Barbels in rapid-waters would be a source of great encumbrance 

 and, therefore, they are much reduced. In most of the hill-stream 

 species they can only be made out after a careful examination. 



Text-fig. 5. — Muscles of the pel 

 Glyptoslermim labiatus. 



The right side of the figure shows the ventral view 

 and the left side the dorsal view of the pelvic girdle. 

 add= adductor muscles ; abd = abductor muscles ; 

 = special muscle. 



