162 DIPTEROUS GENUS DIAPHORUS 



shaped, eyes of the male contiguous, Diaphorus." It seems to 

 me very unsatisfactory to attempt to divide our species by the 

 shape of their wings, and the separation of the eyes alone seems 

 insufficient for the establishment of the genera. 



The following key is based on males only except in one case, 

 that of D. antennatus n. sp. where the first antennal joint is 

 yellow and there is a yellow band at the base of the second 

 abdominal segment ; this female is so distinct from all others in 

 the genus that I have ventured to describe it ; all other species 

 described in this paper are founded on the males only, in many 

 cases it would be difficult to separate the females of allied species, 

 and sometimes not easy to decide whether a female belonged to 

 this genus or was a Chrysotus. Where I could find characters 

 that seemed sufficient to be of any value I have given them after 

 describing the male. 



The characters used for separating the species are, the form 

 of the third antennal joint, this is always of much importance; 

 the general color is used but is subject to considerable variation, 

 even the yellow on the venter and base of the abdomen varies 

 in some species very much, in D. lamellatus Loew some speci- 

 mens show scarcely a trace of yellow even on the venter while 

 others have the venter and a narrow band on the dorsum of 

 the second segment yellow ; the color of the legs is more con- 

 stant, but sometimes where species have yellow tibiae they be- 

 come more or less brownish. The color of the pollen on the 

 head and thorax never varies as far as I have observed. The 

 cilia of the tegulae is subject to much variation in those species 

 having pale cilia, mostly depending on the direction from which 

 it is viewed. I think those species that are placed in the key 

 under "Cilia black" never vary, but if a specimen has blackish 

 cilia and cannot be placed under "cilia black" it should be taken 

 through as "cilia pale" before deciding that it is undescribed. 

 The length of the first vein is a good character used in separat- 

 ing some species. The appendages of the hypopygium are used 

 in a few cases but care should be used not to give too much 

 importance to the length and form of the central filiament or 

 penis as it varies greatly, in D. sodalis Loew, it is usually in- 

 visable but I have seen a specimen where it was very long, the 

 same is true of D. lencostoma Loew, and others ; in life they 

 probably have the power of extending it at will. The width of 

 the face and front is always important. 



