OF WASHINGTON. 95 



pairs of longitudinal slits in the so-called arches ; antennae with 

 one ocellus-like dot ; anterior stigmata sunken, not visible on 

 the outside gen. Gastrophilus 



Larvae in the last stage with membranaceous oral margins, without 

 jaws (very young larvae are cylindrical, with microscopic mouth- 

 parts, between which is a straight process ; in the second stage 

 they have horny oral margins in the shape of a V, with the 

 body behind thin, tail-like) ; two horny rings above the mouth 

 as rudiments of the antennae ; body at anterior end thinner than 

 behind, but sometimes the last ring also very thin ; stigmata on 

 the last ring in the form of horn-like plates, free ; anterior stig 

 mata like minute dots, scarcely visible 2 



Larvae with one pair of jaws, membranaceous oral margins and small 

 membranaceous antennae 3 



2. Spines differently disposed on the upper and under sides ; body much 



less spiny above gen. Hypoderma 



Spines developed and distributed almost alike on the upper and under 

 sides subgen. CEdemagena 



3. Last abdominal segment free, but never deeply cut off from the pre 



ceding one, perhaps forming an appendage, but narrowly joined 

 to the preceding and not drawn within it, posteriorly truncate or 

 deeply hollowed above and elongated into a trunk below ; stig- 

 matal plates on the last segment either free or lying in a cavity 

 formed entirely by this segment, horny ; anterior stigmata 

 small, round, almost button-shaped, horny 4 



Last abdominal segment drawn into the preceding one, much nar 

 rower and shorter than the latter, the larva thereby appearing to 

 have one segment less (in young larvae the last segment often 

 forms a cup-shaped appendage) ; antennae with two ocellus-like 

 dots ; dorsal surface convex longitudinally, ventral surface con 

 cave in the same profile ; anterior stigmata in the form of a long, 

 narrow, transverse slit with wrinkled edges 5 



4. Antennae widely separated at the base ; posterior stigmatal plates 



irregularly 5-sided, roundish, the false opening entirely enclosed 



in the plate ; two ocellus-like dots on each antenna 



gen. CEstrus 



Antennae contiguous at the base, each with two ocellus-like dots ; 

 stigmatal plates moderately free, situated on the slightly con 

 cave, truncate, posterior side of the last segment 



gen. Cephenomyia 



5. Larva oval, thick, densely beset with spurs or scales, only the first 



and last segments' almost naked ; stigmatal plates on the last 

 segment horny, semi-lunar gen. Cuterebra 



