The absence of a distinct ridge, carina or crest on the mesopleura just in front of the middle coxæ, an important structural character first made use of by Kohl, the recurrent nervure in the front wings joining the first cubital cell at or at least nearer the middle than the apex, and the great difference noticeable in the antennæ and the metathorax, readily separate this group from the Crabroninæ.

To me the Thyreopinæ seem to represent a large and distinct group, allied to the others it is true, but yet quite distinct, and divisable into many easily recognizable subgenera. It will be seen also that instead of suppressing the genera erected by some of the older entomologists, which fall into this group, and lumping them with Crabo, as has been done by Kohl and Fox, I have instead recognized all the genera of Latreille, Dahlbom, Lepeletier, etc., and besides have founded some additional genera.