

PSYCHE. 



ORGAN OF THE CAMBRIDGE ENTOMOLOGICAL CLUB 

 EDITED BY B. PICKMAN MANN. 



Vol. I.] Cambridge, Mass., November, 1875. [No. 19. 



On a supposed Case of Seasonal Dimorphism among 



Dspfera. 



Seasonal dimorphism is a constantly recurring disparity- 

 great or small, between two successive broods of the same spe- 

 cies during the same year. The attention of entomologists was 

 recalled to this perhaps too little noticed phenomenon by Dr. 

 Weismann's recent publication concerning some cases of sea- 

 sonal dimorphism among Lepidoptera (Ueber d. Saison-Dimor, 

 phismus d. Schmetterlinge). T am strongly inclined to think that 

 the case I intend to notice here, belongs to the same order of 

 phenomena, among Diptera. It was for the .first time brought 

 forward by me in a recent paper on the genus Syrphus, pub- 

 lished in the Proc. Bost. Soc. Nat. Hist., xviii (Oct. 1875); 

 but I deem it useful to bring it before a larger circle of ento- 

 mological readers, and thus to invite further investigation. 



In preparing the above-mentioned paper on Syrphus, I had 

 the opportunity to examine about "00 specimens of the most 

 common species of this genus in New England, a species 

 closely allied to, if not identical with, the European S. ribesii 

 Linne. The result of this examination was, that I distinguished 

 two well marked forms, each represented in both sexes, and 

 which may be defined as follows : 



I. ' , ? . Eyes pubescent : hind femora black, except at 



the tip ; 



II. $ , $ . Eyes glabrous ; 



i , all the femora black at the base ; hind fem- 

 ora black, except the tip; 



$ all the femora yellow from (lie very base 

 (the coxae being black); hind femora often with a 

 brown ring before the tip. 



