in] FOSSORES Oft DIGGER-WASPS 31 



basal cells, there starts out horizontally a nervure 

 which proceeds towards the tip of the wing. That 

 from the middle of the outer edge of the upper 

 basal need alone concern us : it is termed the cubital 

 nervure. As this cubital nervure passes outwards it 

 is joined to the curved nervure which encloses the 

 marginal cell by one, two, or three short transverse 

 nervures, which thus enclose one, two, or three areas, 

 the submarginal cells, immediately behind the mar- 

 ginal. Now the number and shape of these sub- 

 marginal cells are found to afford very useful characters 

 in discriminating between the various groups of these 

 aculeate Hymenoptera. For example, in Ammophila 

 there are three submarginals, and while in Ammo- 

 phila campestris the third is united to the marginal 

 by a single nervure (petiole] which branches like an 

 inverted letter Y [/J, in A. sabulosa the petiole is 

 absent and each of the two limbs of the A is joined 

 independently to the curved nervure enclosing the 

 marginal cell : in certain other genera there are only 

 two submarginals, one of which is in some provided 

 with a petiole, while in others no such structure is 

 present. But in Crabro there is but one marginal 

 cell in each forewing. Only two other genera of 

 Sphegidae, namely Oxybelus and Entomognathus, 

 have but one submarginal ; and these two are easily 

 distinguished from Crabro ; Oxybelus by the presence 

 of a sharp spike on the back of the hinder part of the 



