Fvssorial Ifymenoptera of North America. 45 



Gengrajili ical Distribution . 



The Crabronidae are very exclusively confined to the north temperate 

 zone, and though more have been described from Europe thus far, it is 

 probable that North America will ultimately furnish as large a uumber. 

 No fossorial hymenoptera, with the exception of the Ants, have been 

 found in the truly Arctic regions. Our collections made in Labrador 

 do not afford a single species. The Canadian fauna, which in the 

 interior of the continent, extends towards the mouth of the Copper- 

 mine and Mackenzie rivers, embraces a few species ; and there area 

 few species, members of the same fauna, which are found at the base 

 of the White Mountains. Southwards, the species have a wide range. 

 The same species occur in New England and the Middle and "Western 

 states alike. Colorado Territory affords another assemblage of species, 

 as do the Gulf states and Cuba, so far as explored. 



Cerceris is a more tropical genus than Crabro or Phihinthus. The 

 Peniphredoninae occur far north in abundance; while the Nyssonidae 

 are most largely developed in subtropical regions, though Oxybehis 

 abounds in the Canadian fauna. In the Arctic and temperate zones 

 where are fewer species than, southwards, these isolated forms are among 

 the most typical, and simple; all bizarre, unusual forms resulting from 

 different modes of coloration and disproportion of parts, being excluded. 

 This tends to make the genera of the Temperate zone more symme- 

 trical and easily limited. As we go into the tropics, Nature becomes 

 more lavish of high, intense colors, and introduces many new modifica- 

 tions of generic form in the different species, so that the tropical 

 genera offer a more heterogeneous mass of species. In the tropics is 

 a greater differentiation of all characters depending on form, size 

 and coloration, as well as habits. Formica is more specialized in its 

 sexual development in the tropics, than in the temperate zone, and the 

 Papilionidse, a truly tropical family, as Wallace* has well shown, have 

 a greater range of variation both in sexual and specific characters 

 than any other family of Lepidoptera. 



Classification, 



In the Crabronites, Latreillef united both the present groups Crabro- 

 nidseand Nyssonidte with the Larridro of Leach. The arrangement is 

 the reverse of modern authors. He places Pemphredon and allies be- 



* Trans. Linnroan Society, Vol. xxv. Pt. 1. 1805. 

 t Genera Crust, et Insectorum, 1809. 



