462 U. S. NATIONAL MUSEUM BULLETIN 216 part 3 



Key to the Nearctic genera of Nematopodiina 



1. Areolet small (fig. 323, a) ; spiracle of first tergite at the middle; cheek about 

 0.3 as long as basal width of mandible .... 1. Messatoporus (p. 462) 



Areolet large (fig. 323,b); spiracle of first tergite near its apical 0.38; cheek 

 about 0.8 as long as basal width of mandible ... 2. Acroricnus (p. 468) 



1. Genus Messatoporus 



Figure 323,a 



Messatoporus Cushman, 1929, Proc. U.S. Nat. Mus., vol. 74, art. 16, p. 8. Type: 

 Mesostenus discoidalis Cresson; original designation. 



Front wing 4.8 to 12.5 mm. long; cheek about 0.3 as long as basal 

 width of mandible; occipital carina complete or its lower end not 

 quite reaching the hypostomal carina; apical carina of propodeum 

 absent; propodeum beyond the basal carina transversely wrinkled, 

 the wrinkling often forming a weak pair of sublateral crests; last seg- 

 ment of hind tarsus without strong bristles at the middle of its under- 

 side; areolet small, almost square; first abdominal segment slender, 

 very little widened apically, its spiracle at the midlength; ovipositor 

 tip depressed, in dorsal view weakly sagittate, the tips of ventral 

 valves enclosing tip of dorsal valve, their teeth varying from coarse 

 and blunt to fine curved ridges. 



Messatoporus is a rather large genus, but with only three species in 

 our fauna. The rest are Neotropic. All species are probably para- 

 sitic in nests of mud wasps. Rearing records are available for only 

 M. discoidalis and M. rujimntris. These parasitize Auplopus and 

 Phanagenia (both Psammocharidae, tribe Macromerini). 



Key to the Nearctic species of Messatoporus 



1. Apical part of antenna compressed, the last 8± segments being about twice 



as deep as wide; hind half of mesoscutum with almost no hairs; middle and 

 hind coxae white, striped with black; clypeus with its apical half quite flat. 



3. compressicornis Cushman 



Apical part of antenna subcylindric; hind half of mesoscutum with moderately 



dense hairs; middle and hind coxae light fulvous, usually whitish dorsally, 



the hind coxa usually with a dorsal fuscous stripe, the middle coxa rarely 



with an apical fuscous spot; clypeus rather evenly convex 2 



2. Median white spot on mesoscutum subcircular, without a white stripe extending 



forward along lateral margin of the median lobe; abdomen usually fulvous 

 or whitish fulvous, more or less banded with fuscous, but never so sharply 

 banded with black and white as in M. discoidalis; oblique groove setting off 

 upper hind corner of mesopleurum without transverse wrinkles; basal 

 0.08± of hind tibia a little darker than subbasal portion ;thyridium on second 



tergite about 0.4 as wide as long 1. rufiventris Cushman 



Median white spot on mesoscutum usually with a thin white stripe extending 

 forward along lateral edge of median lobe; abdomen sharply banded with 

 black and white; oblique groove setting oflf upper hind corner of mesopleurum 



