46 THE BLowFuies or NortH AMERICA 
pleural row of bristles undifferentiated ; lateral postscutellar 
plates setose. 
Wing with fourth vein angularly or roundly bending toward 
wing apex; third costal section nearly as long as fifth and sixth 
together; anterior cross vein usually oblique, near the middle of 
the second section of the fourth vein; posterior cross vein sinuate 
to doubly arcuate, rarely almost straight, considerably beyond 
middle. of third section of fourth vein; last section of fifth vein 
rarely more than one-third as long as preceding section; first and 
fifth veins bare, third with setulae toward base; sixth vein never 
extending to wing margin; seventh vein usually short, and 
straight; lower squamal lobe considerably larger than upper, 
both lobes of medium to large size. 
Legs rarely short, usually of medium length, never ereatly 
modified; fore femur with dorsal, posterodorsal and posteroven- 
tral row of bristles; fore tibia with anterodorsal row of small 
setae; middle femur with posteroventral row of bristles and with 
from one to several anterior bristles near middle; hind femur - 
with anterodorsal and anteroventral rows of bristles; tarsi 
usually as long as corresponding tibiae, rarely modified or orna- 
mented; claws and pulvillae usually as long as proceding tarsal 
septfient. 
Abdomen either broad, round ovate, or oblong ae and ene 
ly more elongate in male than in female; sternites exposed and 
usually overlapping tergites, first usually wider than second; 
ventral membrane rarely narrowly exposed (widely exposed in 
Mesembrinellinae) ; spiracles in tergites; eighth spiracle absent. 
Genital segments of female in form of extensile ovipositor and 
usually concealed in fourth abdominal segment (except in Mes- 
embrinellinae). 
Genital segments of male small to large, often ventral, but 
sometimes terminal to fourth abdominal segment. 
MORPHOLOGY OF ABDOMEN AND GENITALIA. The 
genitalia of the calliphorid flies are of the same general strue- 
ture almost throughout the family and, with the exception of 
those of the females of species of Mesembrinellinae, may be used 
for family distinctions. In this they differ considerably from 
those of the many species of Sarcophagidae in which there is so 
much diversity of form, position, and ornamentation of the vari- 
ous parts. The genitalic structures of the calliphorid flies are 
somewhat difficult to use as a means of specific differentiation. 
While specific differences usually exist, they are not obvious. — 
Since the structure of the genitalia is so similar almost through- 
out the family, it seems unnecessary to describe it for each 
