100 



UNITED STATES NATIONAL MUSEUM BULLETIN 224 



none on the third tergite, and none beyond. Male ter- 

 minalia rotate one-fourth or wholly. The epandrium 

 undivided and uncleft, with a very short, blunt, postero- 

 lateral process. Gonopod smaller, short, broad at base, 

 with narrow, pointed, dorsal process. Hypandrium re- 

 duced to a mere basal lip. 



Distribution: Nearctic: Zabrops tagax Williston 

 (1884). 



I have not seen Triclis fiavipes Jones (1907) from 

 Nebraska or Triclis argentifacies Williston (1901) 

 from Mexico but these species probably belong here. 



Genus Acrochordomerus Hermann 



Figukes 43, 441, 879, 888, 1567, 1602, 1930, 1935 



Acrochordomerus Hermann, Zool. Jahrb., vol. 43, p. 179, 1920. 

 Type of genus : Acrochordomerus aeneus Hermann, 1920. 

 by original designation. 



These are medium size flies of comparatively bare as- 

 pect and short, robust abdomen, belonging to the 

 Laphystini, with only six tergites in both male and 

 female. Very similar in general appearance to Perasis 

 Hermann or Trichardis Hermann but immediately dis- 

 tinguished by character of the antenna. The antenna 

 is elongate, the third segment has two well developed 

 microsegments ; both of these are as wide as the third 

 segment proper and the second is rather long, obtuse 

 apically, with a long, troughlike, dorsal cavity contain- 

 ing a spine. The face with its central depression and 

 ventral gibbosity, together with the type of antenna, 

 strongly suggests the flies of Dioctria Meigen; the re- 

 mainder of these flies in their wing, pile and other 

 characteristics are very like the short-pubescent Laphy- 

 stini. First posterior cell closed; marginal cell nar- 

 rowly closed with bulbous apex. Tergites without spi- 

 nous bristles. 



The hind femur is moderately thickened with short, 

 tuberculate spines or spinous bristles. Pile very short, 

 flat appressed. From Scytomedes Hermann, with its 

 similar face and antenna, it differs by having the extra 

 microsegment and by the tuberculate spines of the hind 

 femur. In Scytomedes the marginal cell is widely open 

 and the proboscis different. Length 14 mm. 



Head, lateral aspect : The length of the head is about 

 three-fourths of the height. The face is slightly pro- 

 duced immediately below the antenna, with a compara- 

 tively low, rounded gibbosity on the lower half and 

 the intervening area distinctly concave. The eye is 

 medium in length, regularly convex anteriorly, and 

 slightly convex posteriorly near the upper comers; it 

 is strongly recessive anteroventrally below, the upper 

 middle portion of the posterior eye margin plane, the 

 eye is also laterally, considerably extended beyond the 

 occiput. Occiput is almost obliterated in profile but 

 rises gently immediately on either side of the foramen 

 and is swollen and bullose posteriorly below the eye 

 on either side of the base of the proboscis. Pile of 

 occiput scanty, moderately long and stiff on the lower 



part but shorter and less abundant dorsally; begin- 

 ning near the middle there are 7 or 8 pairs of weak 

 bristles situated on the upper half. The proboscis is 

 comparatively short ; it is directed nearly straight for- 

 ward and is extended a short distance beyond the face. 

 The proboscis is robust and cylindrical, and distinctly 

 subtruncate ventroapically ; this truncate part bears a 

 lateral fringe of stiff bristly hairs in a single row. The 

 base below has numerous, stiff, long hairs and the basal 

 third is moderately swollen both from lateral and dor- 

 sal view; medial ridge absent. Palpus clearly of two 

 segments, first segment hemicylindrical and excavated, 

 strongly swollen at the base and bearing numerous, 

 long pale hairs. Second segment microporate, cylin- 

 drical, slightly clubbed, bearing 10 or 12 long, yellow 

 hairs but none at apex proper; this segment is set at an 

 angle. 



The antenna attached at the upper fifth of the head, 

 unusually elongate and slender, not quite Vfe times as 

 long as the head. The first antennal segment is a little 

 longer than the second, the third segment (microseg- 

 ments included) is 1% as long as the first two segments 

 combined. The first microsegment is short but distinct, 

 fully as wide as the third segment ; the second micro- 

 segment is more than 3 times as long as the first, slightly 

 more robust, bluntly rounded at the apex and bears 

 dorsally over almost its full length, beginning close to 

 the base, a deep, troughlike or spoon-shaped depression, 

 with a basal spine. First segment ventrally with 1 or 

 2 stout bristles as long as the segment and some other 

 long, stiff hairs; dorsally and laterally it has numer- 

 ous, shorter, bristly hairs; second segment with a few, 

 long setae at apex above and below. 



Head, anterior aspect : The width of the head more 

 than one and one-half times the height. Face below 

 antenna one-fourth the head width, with parallel sides 

 below. Subepistomal area moderately large but nearly 

 horizontal, shallowly concave and bare. The face has 

 scanty micropubescence, the pile is abundant, moder- 

 ately long and stiff on the upper half and curved down- 

 ward ; the sides of the gibbosity have similar pile, the 

 middle and greater part of the gibbosity with numerous, 

 moderately long, stiff bristles. The front is short, 

 largely bare and shining; it is somewhat raised across 

 the middle, with a longitudinal trough or fossa on each 

 side, and bears along the eye margin numerous, weak, 

 bristly hairs. Vertex deeply excavated, with side 

 oblique; the ocellarium is large and high, the ocelli 

 vestigial, and it bears a pair of moderately stiff, slender 

 bristles between the ocelli, set far apart, with in addi- 

 tion posteriorly 2 or 3 other pairs of bristly hairs. 

 Central eye facets considerably enlarged. 



Thorax : The thorax is largely bare, with some micro- 

 pubescence on the posterior mesopleuron, the metapleu- 

 ron, the propleuron, and the hypopleuron. The pile 

 of the mesonotum is abundant but short, curled ap- 

 pressed and setate. Acrostical and dorsocentral bristles 

 not differentiated. There is a narrow, bare, longi- 

 tudinal stripe down the middle of the mesonotum an- 

 teriorly. The following complement of bristles is 



