AMERICAN DIPTERA. 191 



acters mentioned are found to vary considerably in the dif- 

 ferent specimens of the same species." If an attempt is made 

 to separate these two genera by strict adherence to the stated 

 characters confusions result. Among the species listed under 

 Stenopogon in Aldrich's Catalogue three different kinds of 

 antennae are found. The most typical is that possessed by 

 latipe finis and cons anguine us, of which the third segment is 

 elongate, somewhat wider at the middle, and bearing a distinct 

 excision on the inner side from near the middle to the tip (not 

 shown in PI. Ill, fig. 1), and with a comparatively short, thick, 

 but distinct style, itself terminated by a fine, scarcely percep- 

 tible bristle. A second kind is that possessed by hiquinatus, 

 modestus and morosus, of which the third segment is elongate, 

 of equal width throughout, does not bear an excision, and is 

 terminated by a bristle-like style fully half as long as the 

 segment itself. A third kind is that possessed by alibasis and 

 nigritulus of which the third segment is more nearly oval and 

 bears a bristle-like style about one-half as long as itself. This 

 last style of antennse is that which Loew ascribes to the genus 

 Scleropogon and is possessed by helvolus, picticornis and cineras- 

 cens. The last two groups are very closely related from a 

 structural standpoint. The first and fourth posterior cells of 

 these last three species are more frequently closed, although 

 specimens are found in which they are narrowly open. Among 

 the more typical Stenopogons these same cells are more fre- 

 quently open, though often narrowed, closed, and even peti- 

 olate. 



It is, therefore, evident that Stenopogon and Scleropogon 

 cannot be separated by the antennae or the wing venation. 

 The question arises by what character can they be separated? 

 It has been stated* that a comparison of specimens of picti- 

 cornis, with Italian specimens of sabaudus resulted in the firm 

 conviction that the most pronounced difference existing be- 

 tween the two genera is to be found in the nature of the 

 hypopleura, which is bare in sabaudus, but nearly covered 

 with bristles and hairs in picticornis. My observations lead 



* Coquillett, Pr. Ent. Soc. Wash., VI, 179. 



TRANS. AM. ENT. SOC. XXXV. MAY, 1909. 



