NO. 2181. NEW TERTIARY INSECTS— COCKERELL. 377 



Type.—Csit. No. 62537, U.S.N.M. 



The genus Acreotrichus was based ou the Austrahan A. gibhicornis 

 Macquart. The fossil is evidently allied, but generically distinct. 

 Acreotrichus atratus CoquiUett, from the State of Chihuahua, Mexico, 

 appears to represent a third genus; I examined the type some years 

 ago in the United States National Museum. All these flies are very 

 easily known from PhtJdria by the remarkable antennae. The three 

 genera may be separated thus: 



Anterior cross vein much before middle of discal cell; second submarginal cell long 



and narrow, not truncate at base Acreotrichites, new genus. 



Anterior cross-vein beyond middle of discal cell 1 



1. Anterior cross-vein not far beyond middle of discal cell; second submarginal cell 



not truncate at base; third antennal joint about three times as long as the first two 



\Neacreotrichus, new genus (type, Neacreo- 



° [trichus atratus= Acreotrichus atratiis CoquiUett). 



Anterior cross-vein far beyond middle of discal cell; second submarginal cell truncate 

 at base, with an appendicular nervure directed basad from its upper basal corner; 

 third antennal joint not nearly three times as long as first two together. 



Acreotrichus Macquart. 



MESOMYITES, new genus (Empididae). 



Minute flies with narrow wings (shaped much as in Toreus) ; second 

 vein short, directed obliquely upward, reaching costa far from apex 

 of wing; third vein long, simple; praefurca very long; discal cell 

 long, complete, emitting three veins from its apical part; anterior 

 cross- vein near base of discal cell; four posterior cells; lower apical 

 corner of second basal level with apex of first basal cell; anal cell 

 apparently wide open on margin. Third vein obliquely deflected 

 between separation of second and anterior cross-vein. 



Type of the genus. — Mesomyites concinnus, new species. 



MESOMYITES CONCINNUS, new species. 



Plate 31, fig. 7. 



Wing about 3 mm. long, hyaline, veins brown; costa minutely 

 bristly. The following measurements are in microns: Width of 

 wing, 850; basal end of praefurca to apex of wing, 2,144; end of 

 second vein to level of tip of wing, 1,170; upper side of first posterior 

 cell, 1,360; marginal ceU on submarginal, 400; first posterior on dis- 

 cal, 720; first posterior on second posterior, 690; first posterior on 

 wing margin, 128; second posterior on wing margin, 240; second 

 posterior on third, 560; width (depth) of discal cell, 112; discal on 

 second posterior, 80; discal on third posterior, 112; discal on fourth 

 posterior, 640 ; apex (upper apical comer) of second basal apicad of 

 level of apex of first basal, 128. The last 640 microns of anal vein 

 are visible, without any sign of a closed anal cell. At the upper basal 



