AMERICAN DIPTERA. 313 



spines distinct. Wings nearly hyaline; third section of fourth vein 

 three times second. Length, 5.0 mm. ; wings, 7.0 mm. 



Described from Mexico. I have not seen this species. 



40. P. flavicornis Williston. 



9 . Front and face silvery, the former towards vertex shining, very 

 narrow and unusually converging above ; antennae yellow, with third 

 joint obtusely pointed, ovate. Mesonotum dark brown; pleurae sil- 

 very. Abdomen opake, coffee-brown ; first segment gray ; 2-6 broadly 

 opake ; silvery-gray laterally, with more brownish interrupted apical 

 bands. Ovipositor yellowish. Legs yellow, including coxae ; spines 

 conspicuous ; apex of tarsi blackish. Wings nearly hyaline. Length, 

 5.0 mm. ; wings, 6.0 mm. 



Described from Mexico ; the male is also reported from 

 Mexico (1893 Giglio-Toss 71). I have not seen this species. 



41. P. willistoni Kertesz, aculeatus || Will. 



9. Front black, lightly pollinose ; face densely silvery ; third an- 

 tennal joint light yellow, long acuminate. Mesonotum brownish pol- 

 linose. Abdomen shining black ; first segment and lateral margins of 

 following cinereous, ovipositor reddish. Legs light yellow, without 

 femoral spines. Wings nearly hyaline ; third section of fourth vein 

 more than twice second. Length, 3.0 mm. ; wings, 4.0 mm. 



Described from Mexico ; also reported from the West 

 Indies (1896 Williston 351). I do not know the species. 



Subvtrescens-gr oup. 



I have designated by this name a group of several forms, 

 one of which is supposed to be subvirescens Loew. These 

 forms agrees with the typical description of that species in 

 general, but are easily separated from each other by char- 

 acters not given in such description. The females are more 

 difficult to separate than the males. In fact it is sometimes 

 impossible from the present knowledge of the group and 

 from the limited amount of material, to give any satisfatory 

 characters for their separation. The minute, bristle-like 

 hairs near the bases of the femora and trochanters beneath, 

 and also the processes on the latter, are characters which 

 need investigating, and will no doubt throw much light on 

 the classification of this group. Great care is required, and 

 a compound microscope, in the satisfactory examination for 

 these characters, especially the minute hairs. The sculptur- 



TRANS. AM. ENT. SOC, XXXVI. (40) JANUARY, 1911. 



