36 Records of the Indian Museum. [Vol. XXIV, 



in the Eastern Himalayas. In dealing with the fishes of the 

 Manipur Valley I have shown how the fauna of a stream changes 

 within very short limits according to whether the bed is rocky or 

 muddy. Small size is a distinct advantage in hill streams, firstly 

 because the streams are small and secondly because small forms can 

 find more shelter under pieces of rocks and stones during floods. 



2. The scale-covering , etc. — In those Cyprinid fishes that take to 

 hill-stream life, the lepidosis undergoes considerable modification. 

 In the Schizothoracinae the scales are small and partly buried in the 

 skin or are totally absent except in the anal and scapular regions. 

 If in a normal Cyprinid genus in which the scales are large and 

 imbricate, the hill-stream forms be compared with those from 

 other types of environment, it will usually be found that the 

 scales are greatly reduced on the under surface, and in some 

 cases they disappear altogether. The region of the chest, which 

 is to some extent employed in the process of adhesion, is the first 

 to be modified, and then, with the increased rapidity of the flow of 

 water, more and more of the under surface becomes naked. In two 

 species of Garra, G. abhoyai and G. rossictis, the dorsal surface in 

 front of the dorsal fin is also naked. 



The reduction of scales on the lower parts is necessitated 

 ,by the fact that a plain and smooth surface is necessary in order 

 to allow adherence to rocks. I have not been able to understand 

 why the scales should be reduced on the dorsal surface in Garra 

 abhoyai and G. rossicus. Both possess a subcylindrical shape 

 and are not among the most specialized hill-stream forms. 



3. The paired fins and the skeletal and muscular structures con- 

 nected therewith. — The fins are very plastic structures in the anatomy 

 and they have been employed for various functions by diverse 

 groups of fishes. The modifications of the pectoral fins in Flying- 

 fishes, of the first dorsal fin in Sucking-fishes and of the ventral fins 

 in Gobiidae and Gobiesocidae are a few instances among many. 

 In hill-stream fishes the paired fins are used as organs of adhesion 

 or of locomotion and for both these functions powerful muscles 

 are required. In certain cases they are probably used also for 

 respiration. 



The outer rays of the paired fins are employed for the func- 

 tion of adhesion and the number of the inner rays is consequently 

 increased. In Gastromyzon borneensis there are as many as 26-28 

 rays in the pectoral and 20-21 in the ventral fins. In an allied 

 Indian genus, Balitora, there are 21 rays in the pectoral and 11 

 in the ventral fins. The outer rays of these fins are greatly 

 thickened and much flattened. 



Besides an increase in the number of fin-rays of the paired 

 fins, their position and shape undergoes considerable change. The 

 fins, instead of being situated on the under surface of the fish, 

 are pushed outwards and ultimately are placed horizontally on 

 the sides of the body. This change is brought about for two 

 reasons, firstly to allow the ventral surface to be firmly applied 

 to rocks, and secondly to enable the fins to act as organs of adhe- 



