iQ^l.] S. I<. HoRA : Fishes of the genus Gayra. 639 



PROBABLE RVOLUTION OF THE DLSC IN GARRA, AS 



REPREvSENTTED BY A SERIES OF SPECIMENS 



COLLECTED IN MANIPUR, ASSAM. 



The young specimens on which the following observations 

 were made, were collected in various hill-streams that flow into the 

 Manipur Valle}' from the surrounding Naga Hills. I have figured 

 eight stages in the text, seven of which are drawn from the Mani- 

 l^ur specimens while stage 2 is a copy of the illustration previously 

 published by Annandale and myself (1920). The original of 

 I he figure was then referred to Garra nasutns, l:ut I am unable 

 to assign it to any species now on account of the immaturity 

 of the specimen, which is only 74 mm. in length. The Manipur 

 examples are, however, much larger and I have been able to iden- 

 tify them as Gayra yiipccitlus. This is one of the smallest known 

 species of thv' genus and is extremely well-a lapted for life in 

 rapid running streams. The following are the localiti^'s and jnea- 

 surements of these examples : — 



Stage No. I.(nalit\-. 



L'liglh without 

 caudal. 



m m . 



I Small stream, 3 miles N.W. of P(ii*.^nj^ljaum i.V4 



,1 ! Small stream near KangpoUpi i8'5 



4 ! Tliaubal stre.ani near Yaribiik ... 20'o 



,S Sikmai stream near Palel i8'5 



li rii.iubal stroain near Varibuk .. i 2i'o 



1 ■■ i9'(' 



f) ., .. ., ,, . , -'5"" 



It is unfortunate that very little attention was paid to the 

 preservation of these specitnens in the field; 1 was not aware at 

 the time that these young examples would yield such interesting 

 results. The region of the head, however, is well preserved in all 

 the specimens, but the opening of the mouth, which in some ex- 

 amples gapes widely, while in others it is completely closed, consi- 

 derably alters the ventral aspect, especially the extent of the 

 labial folds and the lips. It is clear from the measurements given 

 above that the stages in the development of the disc are not 

 necessarilv correlated with size, but that they may depend upon 

 the age of the fish. We are as yet ignorant of the stimuli that 

 hasten or retard the development of this interesting organ in a 

 particular environment. 



The figures are semi-diagrammatic and are drawn with the 

 help of a camera lucida. 



Great difficulty has been experienced in the terminology of the 

 disc and its associated structures. The mouth in this genus is 

 situated on the under surface and hence the so-called upper and 

 lower lips are really anterior and posterior in relation to the mouth. 

 Moreover the true lips are only visible either in the less advanced 

 species or in the younger stages of the more advanced forms ; with 



