42 
Tur BLOWFLIES OF NortH AMERICA 
3. Metanotum strongly biconvex, the postscutellum well-de- 
fined; edges of sternites usually overlapped and at least 
partially hidden by margins of tergites; abdomen often 
with discal bristles. Larva parasitic upon immature 
stages of insects or warbles or bots in mammals; posterior 
spiracle always with a definite ‘‘button’”’ ....Oestroidea 
and Tachinoidea. 
Metanotum not biconvex, the postscutellum absent or weakly 
developed (if more or less prominent, the metathoracic 
spiracular covering is not in two parts but covers the en- 
tire lower portion, leaving a small opening in the middle 
above); first sternite overlapping lateral margins of 
tergites; abdomen rarely with discal macrochaetae. 
Larva saprophagous, parasitic upon insects or animals; 
posterior spiracles with or without a button.......... 4. 
4. Hypopleuron with weak hair not arranged in rows, or bare, 
the pteropleuron either pilose or bare (if both bare, then 
fourth vein with rounded angle or evanescent). Larva 
saprophagous; posterior spiracular openings short, radial- 
ly arranged, sinuous, or bent (if more or less parallel, 
then with each opening pointed at inner end); rarely 
with distinct fusiform pads on lateral margins of seg- 
TEN ES eo. ban aos yo, Sis As ei ee Muscoidea. 
Hypopleuron setose, with one or more rows of bristles below 
metathoracie spiracle; pteropleuron setose; fourth vein 
usually with a definite angle or bend. Larva saprophagous 
or parasitic upon other animals; posterior spiracular aper- 
tures elongate, usually slender and subparallel; margins 
of posterior depression with tubercles or processes, three 
laterally on upper margin, and generally four on lower 
THAPO Ine sy cme aoe ees APS SC AS oy Sarcophagoidea. 5 
5. Intrapostocular cilia always absent; usually four notopleural 
bristles; spiracle 8 of abdomen sclerotized and located an- 
terodorsally to outer forceps in membrane*; propleuron 
and prosternum usually bare (if pilose, then never with 
long and thick-set pile or hair); arista plumose, pube- . 
— seent or bare, the apex always bare, the plumosity rarely 
long or extending beyound the basal four-fifths; abdo- 
men usually grey or black tessellated, sometimes orna- 
mented with golden pollen (metallic green or blue in sev- 
eral Neotropical genera); greater ampulla usually knob- 
“According to Patton (1934). 
