B52 THE BLOWFLIES OF NortH AMERICA 
slightly petiolate; anterior cross vein oblique, beyond middle of 
second section of fourth vein in proportion 8.5:7; last section of 
fifth vein one-sixth as long as preceding section; both squamal 
lobes with very fine short pile over most of upper surface, the 
lower lobe narrow. 
Abdomen with scutellar depression extending about one-third 
the distance to the hind margin of the first segment; first sternite 
of male small, rounded apically, overlapping margins of tergite; 
second and third sternites smaller and narrower; sternites of 
female as in male but narrower. 
It appears that many of the characters of the species belonging 
to this tribe are in a state of flux, and some of them are so 
variable that they cannot be used for the separation of forms. 
Some of the characters usually considered to be of generic or 
specific value do not appear to be constant enough to allow 
accurate identification of forms through their use. The speci- 
mens are often bilaterally asymmetrical, especially in the pre- 
acrostichal series. As in Pollenia, variation of head parts is so 
wide that it is difficult to draw conclusions as to the exact mean- 
ing of the differences. 
MELANODEXIA WILLISTON 
Melanodexia Williston, N. Amer. Fauna 7 :256, 1893; Manual of 
North American Diptera, p. 355, 1908; Shannon, Wash. Ent. 
Soe. Proce. 28(6) :136, 1926; Townsend, Manual of Myiology, 
vol. 2, p. 260, 1935; ibid., vol. 6, p. 226, 1937. Genarae 
(Melanodexia tristis Williston) = Nitellia glabricula Bigot. 
Monobasie. 
Male and female. Head width only slightly greater than head 
height; length at antenna greater than length at vibrissae; 
epistoma long, slightly narrowed, almost in eclypeal plane and 
gently curved; bucca 0.35 to 0.5 eye height in male, 0.40 to 0.55 
eye height in female; frontale in male narrow near ocelli, wider 
anteriorly, and slightly narrowing again just posterior to lunule, 
but in female three-fifths frontal width at narrowest, striate in 
both sexes; front narrow in male, wide in female, with a few 
scattered hairs outside frontal rows of bristles; frontal bristles 
long and strong anteriorly where the rows diverge widely and 
extend to the middle of the second antennal segment; inner ver- 
tical bristles present; frontoorbital bristles one reclinate and a 
row of about five proclinate in female; vertex with long pro- 
elinate bristles; elypeus only slightly depressed, a little longer 
