Ashmead has lately differentiated eleven families of them.
In his recent classification Ashmead (1901) recognizes seventy-nine families arranged under eight " super-families."
The group of Fossores, or " digging-wasps," is divided by Ashmead, one section forming the Sphecoidea, while the other, together with the Chrysidae Terz!
The Pelecinidae - included here by Ashmead - are large insects with remarkably elongate abdomens and undivided trochanters.
They have usually been reckoned as forming a single, very large family - the Sphegidae- but ten or twelve subdivisions of the group are regarded as distinct families by Ashmead and others.
They are usually regarded as forming a single family - the Apidae - but there is very great diversity in structural details, and Ashmead divides them into fourteen families.
Ashmead, Proc. U.S. Nat.
Ashmead, Historical Sketch of Chester (Chester, 1883).