REPORT ON FISHES. PART I : COBITTDAE 



303 



From the alxive it is clear lliat tl 



lie lonii ami structure of the air-liiaddcr is liable to 

 considerable variation and that the modifications noted above are definitely correlated with 

 the diverse types of habitats. In view of these considerations, and also on account of the fact 

 that all possible gradations exist between different types of bladders, I am of the opinion that 

 the character of the air-bladder should not be used for splitting up species into genera. All 

 the same, it is a good index of the type of habitat of a particular species. 



Caudal Fin: It is well known that in most of the hill-streani fishes the lower lobe of the 

 caudal fin is distinctly longer and better developed than the upper. A powerful stroke from 



Figure 3. Form of caudal fin in the lake inhabiting species of Ncmachilus from Western Tibet, a. 

 Nemachilus vittatus (Heckel). X3; b: Nemachilus panguri, sp. nov. X3; c: Nemachilus hutchinsoni, 

 sp. nov. X; d: Nemachilus deTerrai, sp. nov. X 3. 



such a fin would not only result in the forward movement of the fish but the differential dis- 

 placement of water by the two lolx;s would tend to rotate the anterior end of the fish 

 upwards. This is probably advantageous in the case of torrential fishes when darting from 

 rock to rock in shallow rapid-running waters. By the operation of this device the fish 

 actually moves with its head pointing towards the surface and thus obviates encountering 

 any obstructions in its path. In the torrential species of Nemachilus (Text-figure 2), the 

 caudal loljes are either ecjual or the lower is slightly longer than the upper. I'ut in the case 

 of till- free-swimming "lake" species (Text-fig"ure 3), the u]>pi'r Inbc is Idngcr and better 

 develojjed than the lower. This modification no doubt enables these buoyant fishes to go to 

 the hiittiiui more easily and to keep the head-end directed towards the bottom. The dift'erence 

 in the form of the caudal fin is so marked in the species of the two habitats that it is usually 

 easy to separate, with its help, the specimens with a free air-bladder in the al)dominal cavity. 

 Attention may be directed to the modifications of the air-bladder and the structure of 

 the caudal fin in the species of Nciiuithilus obtained by the Netherland Karakorum Expedi- 



