Rhithrogena 

 semicolorata. 



MAYFLIES, DUNS AND SPINNERS 253 



they may well be ignored by the fly-fisherman. The 



scientific name of this fly is Leptophlebia vespertina. 

 Rhithrogena semicolorata is another fly which is 

 found at times on the chalk- 

 streams, and although I have 

 never found it in an autopsy it is 



quite possible that the trout feed on it. In the north 



country, moreover, it is one of the most abundant of the 



Ephemeridae and has been frequently found in autopsies. 

 In the dun stage the fore- wings are light grey and 



the legs greenish or brownish grey. The spinner 



is very similar in appearance to that of the yellow 



may dun, with which insect 



Yellow upright. it shares the popular name of 



yellow upright. It is, however, 



smaller in size, and may always be distinguished 



by a triangular dark streak in the middle of the 



thigh. 



The smallest of 



all the Ephemeridae 



called Ccenis rivu- 



lorum, is figured in 



Fig. 48. It is seen 



in great numbers on 



the chalk- streams 



on warm summer 



evenings, and some 



fishermen are quite 



convinced that the 



trout take it well at times. Continual observation of 



Fig. 48. C^Nis rivulorum x 6 



