Taxonomic Units of NortH AMERICAN Muscorw Furs 43 
like and round. Larva with dorsal cornua of cephaloskele- 
ton divided or incised; spiracles in deep depression (ex- 
cept in Sarothromyinae); peritreme usually open, the 
‘*putton’’ indistinet or. absent.......... Sarcophagidae. 
Intrapostocular cilia present (except in Rhiniinae and oc- 
casionally in Melanodexia and Onesia); only two noto- 
pleural bristles developed (rarely with an adventitious 
weakened third); spiracle 8 of abdomen absent; propleu- 
ron and prosternum pilose (except in Polleniinae) ; arista 
with plumosity usually long and extending nearly to apex; 
abdomen usually metallic blue, green, bronze, or black; 
ereater ampulla reniform. Larva with dorsal cornua not 
divided or incized; spiracles not in deep depression; peri- 
treme usually closed, the button usually distinct and in 
peritreme (except in Chrysomyinae)....Calliphoridae. 6 
. Metanotum with small but distinct postscutellum; meta- 
thoracic spiracle ovate and very large, the opening on the 
dorsal margin; bucea narrow, hardly one-fifth eye height; 
fourth vein with a broad sinuous curve toward costal mar- 
gin; female without sclerotized and membranous oviposi- 
tor, the larva developed within well-defined uterus. Larva 
with sclerotized area on ventral surface of third seg- 
SAIC eel ee ad L se,» vel atanent Mesembrinellinae, p. 60. 
Metanotum without postscutellum; metathoraciec spiracle not 
as described; bucea distinctly higher in comparison with 
eye height; fourth vein usually with a distinct angle; 
female with sclerotized and membranous ovipositor, the 
larva not developed within a well-defined uterus. Larva 
without sclerotized area on ventral surface of third 
BOO UICULT sass Pp OD Ce Pra gee Te a ee EES amen Aart 7 
Sereeerc Onc iateiabOvelt on: atte He eke cows eke ee lds « 8 
Beer at reraDOVGU- Tr eh Oey een yee aw Fe be wo 9 
. Occipital orbits very narrow; intrapostocular cilia inconspi- 
cuous or absent; greater ampulla either bare or but faint- 
ly pubescent; lower calypter always bare on upper sur- 
face, rounded at apex, the lateral margin nearly straight. 
Third-instar larva with spiracular ‘‘button’’ within closed 
peritreme which extends between each slitlike aperture; 
dorsal cornua of cephaloskeleton having the appearance of 
DEM aIvIGed. Coles es 2 eee apart 6 .. Rhiniinae, p. 89. 
