AMERICAN DIPTERA. 149 



Legs. — The legs are comparatively long and stout, but show 

 variation in robustness in different genera. As a rule they 

 are well armed with bristles and pile; too variously so to re- 

 ceive attention in this regard here. In some of the more 

 delicate species the legs are clothed with hair-like bristles, but 

 in all of the larger, strong flying species, the bristles are stout 

 and strong. The coxae are always well developed and their 

 basal articulations with the body are close together; the fore 

 pair are ordinarily heavily clothed with bristles or hair on the 

 anterior side, the posterior pairs less so on the outer and lower 

 sides. The trochanters are easily distinguished but very small. 

 The three pairs of legs vary little from each other in general 

 size and shape; the posterior femora are often slightly more 

 robust, and in some species of Leptogaster often extremely 

 attenuated proximally and distally prominently swollen, char- 

 acteristics not possessed by the anterior pairs or by the usual 

 Asilid femur. The tibiae are of nearly equal length with the 

 femora, for the most part slender but stout ; but the hind pair 

 may be characteristically swollen as in species of Holopogon 

 and Holcocephala, and the fore pair in such genera as Deromyia, 

 armed on the inner side with a terminal claw-like spur (PI. 

 II, fig. 3; PL VI, fig. 3). The tips of the middle tibiae are 

 usually armed with bristles directed downward (PI. II, fig. 4). 

 In Chrysoceria and Callinicus they possess two prominent 

 bristles not only directed downward, but distinctly inward as 

 well (PI. II, fig, 5 ; PI. VI, fig. 6). 



There are five tarsal segments, the first noticeably longer 

 than the fifth, and called the metatarsus. In species of Hol- 

 opogon and Holcocephala, the hind metatarsus is unusually 

 enlarged. The fore tarsi are sometimes noticeably elongate 

 as in several species of Cyrtopogon, the last tarsal segment 

 bears two strong curved claws, between which there is a well 

 developed bristles-like spine, the empodium, except in two 

 species of Leptogaster where it is vestigial. The two pulvilli, 

 leaf-like appendages beneath each claw, are well developed, 

 about three-fourths as long as the claws, and usually of a 

 pale color; they are vestigial in the species of Ablautus and 

 Leptogaster. 



TRANS. AM. ENT. SOC, XXXV. APRIL, 1909. 



