542 PROCEEDINGS OF THE NAjTTONAIL MUSEUM vol. 93 



of propodeum one-half as great as length of mesoscutellum ; gaster as 

 long as or slightly longer than thorax. 



Male. — Length, 1.1 mm. Darkened anterior carina of scape minute, 

 located at a point one-third the distance from apex to base of scape, 

 pedicel one and two-thirds times as long as first f unicle segment, second 

 segment almost twice as long as first, third and fourth equal in length 

 and each slightly longer than second, club two and one-half times as 

 long as fourth f unicle segment; f unicle segments bearing conspicu- 

 ously long bristles on elevations near bases of segments ; marginal vein 

 of forewing three and one-half times as long as stigmal, fringe at 

 posterior margin of hindwing one-half as wide as wing at hamuli; 

 gaster slightly longer than thorax. 



Type locality. — Fairy Lake, Gallatin County, Mont. 



Types.— U.S.N.M. No. 56212. 



Described from 1 male and 10 female specimens, as follows: Female 

 holotype, male allotype, and 1 female paratype from the type locality, 

 reared from Trioza sp. nymphs on Angelica lyalli, September 4, 1939. 

 D. J. Pletsch ; 2 female paratypes having the same locality, date and 

 collector as above, but taken sweeping vegetation infested with unde- 

 termined psyllids; 5 female paratypes, same locality, date and col- 

 lector, but reared from Trioza sp. nymphs on Thalictrum occidentale ; 

 10 female paratypes, Bozeman, Mont., reared from Trioza sp. nymphs 

 on Salix sp., September 23, 1939, D. J. Pletsch. 



TETRASTICHUS TRIOZAE, new species 



Figurfs 16, i, i; 20, d 



Black, non iridescent; apices of scape and pedicel and variable areas 

 of flagellum, wing veins, bases and apices of femora and tibiae, and 

 basal segments of tarsi white or light yellow ; anterior tibiae usually 

 darkened only on outer face ; base of gaster sometimes tan ; antennae 

 and legs of males sometimes entirely white or light yellow. 



Female. — Length, 0.95-1.05 mm. Antennae inserted slightly ven- 

 trad of level of ventral margins of compound eyes; scape short, its 

 apex reaching a point only two-thirds the distance from clypeal mar- 

 gin to anterior ocellus; pedicel one-half as long as scape, each f unicle 

 segment shorter and wider than that proximad of it; third segment 

 three-fourths as long and one and one-third times as wide as first, 

 maximum width of club almost twice as great as width of third f unicle 

 segment (fig. 16, i) . Mesopraescutum with two bristles at each lateral 

 margin ; submarginal vein of forewing with one dorsal bristle, stigmal 

 vein one-third as long as marginal; apex of hindwing acute, fringe at 

 posterior margin one-half as wide as wing at hamuli. Surface of 

 propodeum almost smooth, faintly reticulated and with median carina 



