138 NORTH AMERICAN DIPTERA. 



LARVAE. 



1. Last abdominal segment free, broadly attached 2 



Last abdominal segment (twelfth) retractile within the preceding, small 



and distinctly constricted. 7 



2. Larvae with two pairs of chitinized jaws, that is with two outer mouth- 



hooklets, and two inner, straight, triangular points (Horses). 



GASTROPHILUS. 

 Larvae with two or no mouth-hooklets , . 3 



3. Larvae on the median segments with dorsal, spindle-shaped tubercles ; 



one pair of mouth-hooklets present 4 



Larvae without such tubercles ; one pair or no mouth-hooklets present. 5 



4. Antennae broadly separated ; body oval, strongly convex above, flat be- 



low (Sheep) CEsxRus. 



Antennae approximated or contiguous ; body elongated, somewhat 

 broader in front than behind (Deer). . . . CEPHENOMTIA. 



5. No mouth-hooklets.. 6 



Two small mouth-hooklets present (Rodents). . . (ESTROMYIA. 



6. Bristly covering alike above and below (Reindeer). . (EDAMAGENA. 

 Bristles stronger below than above (Ox, etc.) . . HYPODERMA. 



7. Larvse oval (Rodents, Marsupials) CUTEREBRA. 



Larvae club-shaped, more slender posteriorly (Artiodactyls, Carnivora, 



Primates) . . . DERMATOBIA. 



54. SARCOPHAGIM;. 



Usually thick-set, moderately large to rather small flies. 

 Front in both sexes broad, though usually somewhat narrower 

 in the male. Arista of the antennae plumose to the middle or 

 a little beyond, the distal portion bare ; this last character 

 alone is the ultimate distinctive one of the group. Abdomen 

 composed of four visible segments, with the macrochaetae 

 usually confined to the distal portion, though sometimes occur- 

 ring on the margin of the second and following segments and 

 very rarely on the disk ; male hypopygium often prominent. 

 First posterior cell of the wings always much narrowed or 

 closed. 



This family of flesh-flies, as they are often called, though 



