170 Records of the Indian Museum. [Vol. XXII, 



sluggish stream in almost level country. During my tour I was 

 able to make collections from the same stream at different places 

 where the bed was sometimes rocky and sometimes muddy. For 

 example I made a collection in the Thaubal stream near Yari- 

 huk where it is muddy and sluggish and in the same stream about 

 I mile from Phadai, where it flows rapidly over a rocky bed. 

 vSimilarly in Sikmai Stream I made collections at two different 

 places, one near Vabgai in tlie valley and the other near Palel 

 some six miles from Kakching \illage, where the stream may be 

 called a torrent. A comparison between the species obtained from 

 the latter stream in the two places is instructive. 



It will be observed that examples of Garra and NemacMIiis, 

 the only genera that exhibit adaptations to life in hill-streams, are 

 found at Palel where the water flows rapidly over a rocky bottom, 

 while those of Lepidocc phalicldliys and Macrones that prefer a 

 muddy bottom are only found near Vabgai where the stream is 

 sluggish and muddy. The remaining two species, belonging to 

 Acanthophtlialmus and Crossochilus. are capable of existence under 

 both conditions. 



The greatest specialization is found, however, among those 

 fish that actually live in rapid waters. In the species of the genus 

 Barilius, the paired fins are greatly expanded and some of their 

 outer rays have become very strong. In older specimens definite 

 muscle-pads are developed ou either side of the chest in front of 

 the bases of the pectoral fins. In loaches the mouth is specialized 

 to form a sucker, and by the help of its thick lips the fish are 

 enabled to stick to stones and withstand rapid currents. In N. 

 sikmaiensis the mouth is not specialized, but this is compensated 

 for by the higher specialization of the paired fins which are greatly 

 expanded and are provided with muscles on their ventral aspect. 

 The disc of Garra and the chest-muscles of GlyptotJiorax are ex- 

 amples of extreme modifications due to adaptation to a particular 

 environment. 



GEOGRAPHICAI, RELATIONS. 



The fish dealt with in this paper belong to two watersheds. 

 The line separating these is a ridge some three miles from Kairong, 



