THE GENTJS TACHTNOMYIA — ^WEBBER 295 



The following brief description is from a cotype, Sonoma County, 

 Calif., now in the United States National Museum collection: 



Male. — Front and face silvery gray pollinose without trace of yel- 

 low ; fourth abdominal segment mostly black, mottled gray pollinose ; 

 cheeks nearly one-half of eye height, clothed with comparatively 

 long hairs which are predominantly black; hind tibia with short 

 villosity on inner side; frontalia wider than either parafrontal; 

 bristles of facial ridges strong, reaching two-thirds way to antennae; 

 lobes of fifth sternite reddish, without basal flange but with slight 

 ridges; apex of fourth sternite convexly produced: three dorsocen- 

 tral bristles; no posterior preintraalar bristle; anal forceps (fig. 

 17. c) somewhat as in nigricans: second genital segment orange-red; 

 second antennal segment black. 



Forty-one other males in the United States National Museum col- 

 lection agree well with the cotype. There are usually three dorso- 

 central bristles although occasionally four are present : posterior pre- 

 intraalar bristle absent in all but two specimens, in which case it is 

 vestigial; facial ridges bristly two-thirds way to antennae, rarely 

 less; vibrissae well above oral margin; scutellum wholly black, fre- 

 quently with reddish apex; face and front silvery gray pollinose 

 without trace of yellow; usually three strong bristles on anterior 

 dorsal side of middle tibia. 



Female. — Essentially like male except for the usual sexual 

 differences. 



Variations. — Twenty-one males and 27 females bred by the writer 

 from Stajmotia solids Linnaeus, collected at Puyallup, Wash., in 

 1935. show the following variations: Three or four dorsocentrals, 

 usually the latter, although very frequently the second from the 

 suture is either weak or hairlike. When three bristles are present 

 they are often irregularly spaced. Posterior preintraalar bristle 

 absent in 39 and vestigial in 9. Second genital segment of male 

 orange-red in all but two specimens, in which case it is obscurely so. 

 Abdomen wholly black, gray pollinose or frequently, in the male, 

 with sides of second segment reddish yellow: second antennal seg- 

 ment black. Face and front silvery gi'ay pollinose in all specimens. 

 Length, 12-13 mm. 



Material examined. — About 90 specimens at the United States 

 National Museum from localities in California, Washington, Idaho, 

 Oregon, Colorado, and Arizona. 



Hosts. — CUsiocamjya thoracia Stretch : Eemerocam/pa vefusta Bois- 

 duval; Stilpnotia f^oIicU Linnaeus; Ualhidota argentafa Packard. 



