1922.] S. h. Hofa : Fish of Mountain Torrents. 35 



met with in the pools. Of these genera only smaller forms like 

 Danio rerio are usually found, for they alone are able to find during 

 the flood season sufficient shelter underneath rocks and stones. 

 The pools are, however, sometimes inhabited by large species of 

 Barbus and Barilius which are sufficiently powerful to withstand 

 floods. 



MODIFICATIONS FOR LIFE IN HILI,-STREAMS. 



The modifications for life in hill-streams may be considered 

 under the following heading : — 



1. The external form of the fish and its size. 



2. The scale-covering, etc. 



3. The paired fins and the skeletal and muscular struc- 



tures connected therewith. 



4. The caudal fin and its peduncle. 



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



barbels, the lips and their muscles. 



6. The eyes. 



7. The gill-openings, brauchiostegal rays and mem- 



branes. 



8. The air-bladder. 



9. Special modifications of the skin. 



1. The external form. — Nikolsky (cp. cii.) has dealt with this 

 subject but as the text of his paper, which I have not seen is in 

 Russian, I give my own observations in full. The fish with which 

 this paper is concerned all live on the bottom, and the form is 

 so modified as to offer the least resistance to the rapid current. 

 The head and body are greatly flattened and in Balitora, GlyPto- 

 stemum and in the most specialized hill-stream species of Garra 

 and Glyptothorax the form is almost leaf- like. The ventral profile 

 becomes straight and horizontal throughout and the dorsal profile 

 is but slightly arched. The head is usually small and semicircular 

 and the snout is trenchant. The Bornean genus Gastromyzon is in 

 shape a typical hill-stream form. 



The shape of the bod}^ depends upon the strength of the 

 current and any deviation from the characteristic form of the fish 

 is directly proportional to the rate of the flow of water. Thus 

 the form of those fishes that live in places where the intensity 

 of the flow is intermediate between that of a sluggish stream 

 and of a hill-torrent is almost cylindrical, as in Crossochilus latia. 

 Confining our attention to the members of the genus Garra, one 

 can find all possible gradations in shape between such forms as 

 Crossochilus latia and the most soecialized h ill-stream form such 

 as Balitora. Garra tnullya, one of the most widely distributed 

 forms in the genus, lives in ponds, tanks and sometimes in rapid 

 waters. The specimens collected from ponds and tanks are 

 cylindrical, while those collected from rapid w r aters are sometimes 

 flattened. Great modification in form is exhibited by G. lissorhyn- 

 chas, G. kempi and G. nasutus, all of which are known from rapids 



