212 U. S. NATIONAL MUSEUM BULLETIN 216 



X. TIBIALIS GROUP 



Front wing 3.2 to 7.5 mm. long; head about average for the genus, 

 the temple moderately long, cheek short, and face moderately to 

 rather strongly convex; interantennal process blunt to acute; median 

 part of frons very weakly to strongly differentiated and protuberant, 

 rarely with a high median ventral ridge; occipital carina absent or 

 present laterally as a weak vestige; median 0.6 of clypeal margin 

 straight or weakly concave; head black, the face usually mostly or 

 entirely white or yellow but sometimes entirely black; orbital marks 

 on frons usually absent or incomplete, rarely complete; spot at top 

 of eye usually large, but rarely vestigial or absent, subtriangular, 

 adjacent to eye; notaulus moderate, rather short; metapleurum rarely 

 with a few discal hairs ; costula present or absent ; median longitudinal 

 carinae and apical transverse carina of propodeum complete, the 

 median longitudinal carinae strongly bent inward just basad of posi- 

 tion of costula; second lateral area of propodeum with hairs in its 

 apicolateral corner and usually also some hairs laterally, usually bare 

 elsewhere; nervulus beyond basal vein; front spur of middle tibia 

 0.4 to 0.6 as long as hind spur; second segment of middle tarsus 1.0 

 to 1.5 as long as wide; hind tibia sometimes uniformly colored but 

 usually infuscate apically and often infuscate basally, never with a 

 subbasal infuscate band; first tergite 1.4 to 2.5 as long as its width 

 at basal corners; second tergite about 0.6 to 1.6 as long as wide, with 

 moderate-sized, rather sharp punctures that are sparse or absent on 

 median part of tergite; epipleurum of third tergite sub truncate 

 apically, its inner margin evenly arcuate or strongly arcuate basally 

 and almost straight postmedially. 



This group is the dominant one in the Holarctic region. We have 

 seen also a few representatives from the Oriental and Neotropic 

 regions. Thirty-three Nearctic species are described below and there 

 are doubtless many more to be discovered. The Palaearctic species 

 that we have seen and would assign to this group are: Exochus alpinus 

 Zetterstedt, 1838 ;E. lentipes Gravenhorst, 1829; E. semilividus Vollen- 

 hoven, 1875; E. suishanus Uchida, 1932; E. tardigradus Gravenhorst, 

 1829; 2?. thomsoni Schmiedeknecht, 1925; and E. tibialis Holmgren, 

 1856. 



21. Exochus annulicrus Walsh 



Figures 189,h; 193,b 



Exochus annulicrus Walsh, 1873, Trans. Acad. Sci. St. Louis, vol. 3, p. 95; &. 

 Type: d\ ?Illinois (destroyed in Chicago fire of 1871). 



Front wing 3.5 to 4.5 mm. long; combined face and clypeus 1.10 as 

 high as wide, evenly convex, the horizontal convexity a little greater 

 than the vertical convexity; facial punctures of median size, sharp, 



