1927] 
Observations on Wood-boring Insects 
81 
are fused. This similarity is however purely superficial. Con- 
sidering the wide divergence between the two groups we must 
conclude that the reversed mandibles are of independent origin 
and that this peculiarity has developed more than once in the 
order Hymenoptera. 
The similarity in venation between Yanhornia and Helorus 
is very great and in fact there is no difference except that Helorus 
has lost the upper section of the basal vein which is still present 
though weak in Vanhornia. Ashmead speaks of the basal vein 
as bent down to form a discoidal cell in Helorus but this vein is 
a combination of the lower section of the basal and the first 
section of the cubitus which form together an arc as is readily 
seen by comparison with Vanhornia or Ropronia. Ropronia was 
placed by Ashmead as a part of the family Heloridse and I think 
correctly so although Bradley has disputed this. Ropronia again 
agrees closely with both Helorus and Vanhornia in venation. 
Aside from the peculiarities of the head associated with the 
greatly enlarged mandibles, the complete reduction of the ab- 
dominal petiole and the greatly developed ovipositor, Vanhornia 
is clearly similar to Helorus and the Jurassic genus Meso helorus 
and the two families must be placed near together in the group 
Serphoidea. Handlirsch following Viereck has placed Vanhornia 
next to the Alysiidse and the strange genus Gnathobracon. 
This position appears to be clearly untenable as noted above. 
Family Chrysididce 
Chrysis verticalis Patton. One female, September 26. 
Omalus iridescens Norton. Four specimens, July 17-26. 
Species of Omalus are parasitic upon wasps that nest in wood 
0. corruscans has been bred from Stigmus americanus which is 
probably the host of the present specimens. 
Family Eumenidoe 
Odynerus cristatus Saussure. Nine specimens, July 18-28. 
This is a common species nesting in burrows in wood. 
