20 V. S. NATIONAL MUSEUM BULLETIN 216 paet 3 



Key to the sub tribes of Mesostenini 



1. Mandible about 4.5 as long as its width at the middle, its upper tooth much 



longer than its lower tooth, the lower tooth sometimes indistinct; clypeus 

 broad, its apical margin broadly truncate or concave, without a median tooth 

 or lobe; first abdominal segment slender, only a little widened apically. 



3. Nematopodiina (p. 461) 

 Mandible about 1.5 to 3.5 as long as its width at the middle, its upper tooth 

 not or little longer than its lower tooth; clypeus usually narrower, its apical 

 margin various, often with a median tooth or lobe; first abdominal segment 

 various, usually stouter and apically more strongly widened. (Rarely, as 

 in Compsocryptus buccatus, the mandible is as described for the Nematopo- 

 diina, but in these exceptions the first abdominal segment is stouter and 

 more distinctly widened apically.) 2 



2. Wings of normal size, longer than thorax 3 



Wings abnormally small, shorter than thorax 6 



3. Ovipositor not surpassing tip of abdomen; female subgenital plate broad, 



rhomboidal, weakly convex; second intercubital vein absent, not present 

 even as a trace. (In Sphecophaga, the only Nearctic genus, the first inter- 

 cubital is about 6 times as long as its width. In the other Nearctic Meso- 

 stenini that lack the second intercubital, the first intercubital is relatively 



shorter.) 5. Sphecophagina (p. 522) 



Ovipositor nearly always surpassing tip of abdomen; female subgenital plate 

 not large and rhomboidal; second intercubital vein usually present, if absent 

 there is usually a trace left 4 



4. Spiracle of first tergite at, a little in front of, or a little behind the middle; 



lower valve of ovipositor near apex with a dorsal lobe that encloses or partly 

 encloses upper valve of ovipositor (fig. 329,p) (except in Helcostizus and in 

 some species of Echthrus); ovipositor compressed; front tibia of female in- 

 flated, suddenly constricted at base; fourth tarsal segment of female with a 

 dense apical group of stout bristles on the under side, the apical margin 

 of the fourth tarsal segment not or very weakly bilobed; apex of female 

 fiagellum more or less truncate. (This group is easy to recognize in the fe- 

 male but more difficult in the male. Males of all Nearctic genera except 

 Xylophrurus may be distinguished from the Mesostenina and Bai-yceratina 

 by the fact that the spiracle of the first tergite is at or in front of the mid- 

 dle. Xylophrurus males may be distinguished by the combination of a small 

 clypeus (about 0.5 as wide as face) with a sharp median apical point, and 



the large pentagonal areolet.) 4. Echthrina (p. 476) 



Spiracle of first tergite varying in position from a little behind to far behind 

 middle; lower valve of ovipositor near apex without a dorsal lobe that en- 

 closes or partly encloses upper valve of ovipositor (except in a few exotic 

 genera: Kriegeria, Amauromorpha, Dotocryptus, and an undescribed Neotropic 

 genus); ovipositor cylindric or more or less compressed; front tibia of female 

 usually not inflated but sometimes moderately inflated; fourth tarsal segment 

 of female either without a dense apical group of stout bristles on the under 

 side, or if it has such bristles the apical margin of the segment is bilobed; 

 apex of female flagellum a rounded point 5 



5. Upper valve of ovipositor with a series of teeth or transverse oblique ridges 



between nodus and apex; flagellum usually rather short and thick; thorax 

 usually rather short and thick. (This group is easy to recognize in the fe- 

 male but not in the male. In the Nearctic region there are only two genera: 

 Whymperia and Baryceros. Since males of these may easily be mistaken 



