A REVISION OF THE GENUS HYDRIOMENA 

 BASED ON THE MALE GENITALIA 



Mr. L. W. Swctt in liis notes on this genus (1911, C. Ent. 43, p. 7i; 

 1912, C. Ent. 44, p. 225 ; 1915, C. Ent. 47, pp. 9, 58) has clone valuable 

 work in separating our North American species, his subdivisions into 

 short, moderate and long palpal groups being a distinct advance over 

 anything heretofore attempted in the classificatory line ; personally we 

 have never favored his color-pattern scheme, it has seemed to us too 

 artificial and we have always had the feeling that a number of his 

 so-called forms might, on further study, prove to be good races or even 

 species, a theory which has been amply borne out by our studies. It 

 is greatly to be regretted that Mr. Swett's work was, as he himself 

 states, more or less unfinished; his inability to examine and compare 

 the i genitalia of the various species involved has, we fear, led him 

 into several rather serious errors which we feel sure would have been 

 eliminated if he had had the opportunity to work out the structural 

 details of the genital organs. 



We recently had occasion to examine the genitalia of a number of 

 species in this group and the results were so startling that we decided 

 to extend our investigations to all the species contained in the genus ; 

 we were primarily struck by the excellent means of separation afforded 

 by the shape of the Uncus which is all the more important as, generally 

 speaking, this portion of the genitalia may be examined under a strong 

 lens or binocular by simply removing a few hairs with a fine brush 

 from the dorsal portion of the anal segment ; the necessity for breaking 

 off any portion of the abdomen and the consequent mutilation of choice 

 specimens to establish their identity is thus obviated and. while not 

 always conclusive, the general results obtained by such an examination 

 are eminently satisfactory, especially if taken in conjunction with the 

 palpal length of the species in question. 



In the following notes we give the result of our investigations, and 

 would take this occasion to extend our thanks to Mr. Swett for his 

 hearty co-operation. We are also greatly indebted to the authorities of 

 the American Museum of Natural History for the loan of their entire 

 material in this genus which, containing as it does several hundred 



