314 E. T. CRESSON, JR. 



ing of the abdomen, in some species, can be distinguished 

 only under a magnification of about 60-70 diameters. The 

 black hairs on the abdomen seem to vary considerably in 

 density, size, and inclination, and although they may prove 

 to be of some importance, I have not given them much atten- 

 tion here. No doubt politus Williston, belongs in this group, 

 but the description is inadequate for closer determination. 



42. P. subvirescens Loew. 



Dr. Hough redescribes this species from Loew's type as 

 follows : 



Front of male very small, silvery pollinose, without depression ; 

 eyes in contact. Thorax and scutellum shining greenish-black, dusted 

 with brown pollen in the middle and towards the cephalic border ; 

 humeri yellow ; halteres with yellow knob and brownish peduncle. 

 Abdomen greenish-black, shining, with delicate whitish hair or almost 

 naked ; hypopygium small, hardly half as long as the fifth segment ; 

 its rima oblique and to the right of the median line ; terminal piece of 

 ovipositor straight and about as long as the hind tibia. Legs black ; 

 the apex of the femora and base of tibiae yellowish ; tarsi brownish- 

 yellow, towards the tip black. Wings hyaline; veins black; stigma 

 not colored ; fourth costal section hardly twice the third ; small cross 

 vein at or apicad the middle of discal cell. 



I have only a male before me which agrees with this de- 

 scription. This one is rather old and more or less faded in 

 color, bearing a label marked " Md." The front has a yel- 

 lowish tinge ; antennae brownish, long white acuminate ; ab- 

 domen narrowly ovate, as wide as thorax at third and fourth 

 segments,' shining, at most grayish tinged only at base ; fifth 

 segment longer than fourth, with a large dorsal indentation ; 

 sparsely clothed with delicate light colored hairs which are 

 hardly visible. Hypopygium much shorter than fifth (Fig. 

 104), and about one-half as wide, somewhat assymetrical, 

 but regular in outline, cleft, much more developed beneath, 

 with the intermediate lobe broad. Post-trochanters with 

 tufts of minute hairs on a weak tubercle at bases beneath 

 (Fig. 130). Length, 2.5 mm.; wings (Fig. 175), 2.8 mm. 



As to the species aridus Williston, and translahis Walker, 

 I cannot do better than treat them as synonyms of this 

 species as does Dr. Hough (1899 Hough 78). 



