AMERICAN DIPTERA. 153 



Terminal segment of antennae elongate, and densely microscopically 



pubescent (PI. VII, fig. 1) CeraturgUS. 



i. Style of antennas short, thick, obtuse, not easily distinguishable 

 from the third segment, or if so forming apparent joints; 



antennas more or less elongate 19. 



Style of antennas small, more slender than the third segment, 



apparent; antennas usually shorter 21. 



'. Nearly bare species; face flattened, bare, except below, small or 

 rather small species, polished or metallic black, with narrow 



or cylindrical abdomen and large wings 20. 



Thickly or rather pilose species, the bristles few and hairdike; 

 antennae inserted on a convexity, the facial profile thence 

 receding to the tubercle which is situated upon the lower 

 part of the face; abdomen moderately stout; head narrow 



(PI. IX, fig. 2) Dicolonus. 



). All the tibiae and hind femora with short strong bristles (PI. VIII, 



fig. 6) Echthodopa. 



Hind femore without such bristles (PI. IX, fig. 8) Dioctria. 



.. Face distinctly swollen in profile, usually gibbose 22. 



Face flattened, or gently convex 23. 



!. Usually thickly pilose species (*); the gibbosity of the face reaches 

 to the base of the antennae; anal cell usually open (PI. VIII, 



fig. 1; IX, 1, 7; X, 6) Cyrtopogon. 



Thinly pilose, more pruinose species, the convexity of the face 

 confined to the lower part ; anal cell usually closed (PI. 



IX, fig. 6) Lasiopog-on. 



i. Bristles of mesonotum arranged in distinct rows, see Metapogon. 



Bristles not so arranged 24. 



:. Abdomen elongate; front broad anteriorly, narrowed behind (PI. 



VI, fig. 5) Plesiomma. 



Front not narrowed behind 25. 



i. Hind tibiae toward the tip and their metatarsi much thickened, 26. 

 Hind tibiae not, or but slightly, thickened toward the tip; their 



metatarsi not thickened 27 . 



i. Head much broader than high, transverse "goggledike" (PI. V, 

 fig. 4); abdomen short, wings large (PI. XI, fig. 6). 



Holocephala. 

 Head only moderately broader than high, not at all spectacledike 

 in appearance (PI. V, figs. 5) (PI. XI, figs. 1, 2). 



Holopogon. 

 '. Style of antennae long and slender, at least onedialf as long as the 



slender, tapering, third segment; quite stout species 28. 



Style of antennae not one-half as long as the third segment and 

 stouter than above 29 . 



(*) For exceptions, note PI. IX, fig. 1, and PI. X, fig. 6. 



TRANS. AM. ENT. SOC, XXXV. (20) MAY, 1909. 



