'i'8 INSDCUTOR INSCITI^ MENSTRUUS 



ish to near apex; first tarsal joint pale, black at apex, second 

 joint with the basal third pale. Hind legs with the femora 

 mostly blackish, the tibiae whitish to near the middle, black 

 beyond; tarsi with the first joint white basally, black beyond 

 the middle, the second and third joints basally white. Claws 

 simple, slender. Wings hyaline, the venation normal, the 

 coarse veins brownish yellow, the membrane slightly milky, 

 iridescent, but without differentiated iridescent area in the anal 

 field. Halteres pale yellow. 



Length : Body about 2 mm., wing 2.3 mm. 



Arlington, Texas, October 28, 1914 (F. C. Bishopp, No. 

 1938) ; 12 specimens. 



Type: Cat. No. 19635, U. S. Nat. Mus. 



Closely related to Simulium griseum Coquillett ; that species 

 differs, among other characters, in the ferruginous scutellum and 

 in the paler legs, the femora and tibiae of the middle pair being 

 wholly yellow, those of the front legs with only the apices 

 tinged with ferruginous. The male of 5. griseum shows dis- 

 tinct broad blackish median and sublateral stripes on the 

 scutum, but in a series of females before me (including the 

 three type specimens from Colorado) the scutum is almost 

 uniformly light gray, without trace of median pigmented stripe 

 and only a median impressed line ; only one specimen shows a 

 faintly darker median stripe; there are broad whitish lateral 

 margins, absent in mediovittatum ; the two white spots on the 

 anterior margin of the scutum are larger and more distinct in 

 griseum. 



Simulium mediovittatum shows considerable variation in the 

 thoracic coloration. The ground-color of the scutum varies 

 from a very pale gray to a darker gray with distinct bluish 

 or greenish blue cast. The median stripe varies from reddish 

 brown through deep brown to black, and is rather broad, 

 although slightly variable in width. The sublateral stripes are 

 obsolete in the darker specimens and in some lights the extreme 

 lateral margins show broadly dark ; the whitish anterior spots 

 are also obsolete in the darker specimens. 



