135 



Xesoprosopis was separated In- Dr. Perkins largely ou the 

 character of the eight stemite of the S aud this does not seem 

 to me to be so strongly different from some species still re- 

 maining in the old genns Prosopis. 



He supplements this character by the lack of enelosnre of 

 the basal area of the propodeum. Most of the species have 

 absolutely no clear line bounding this area. However the 

 area is clearly defined in some of the species such as N. 

 fuscipennis (Smith) and N. pubescens Perkins. 



I am inclined in studying the Hylaeidae to give consider- 

 able importance to the structure of the supraclypeal area and its 

 extension above between the antennae. While frequently it is 

 not easy to describe this structure, it seems to be very charac- 

 teristic in the different groups. In this character Nesoprosopis 

 differs from Hylaeus in the more limited sense which I should 

 use it. In Nesoprosopis this area is convex between the anten- 

 nae and narrowed, rounding down at the sides to the rest of 

 the surface without angles, ridges or carinae; it is also not 

 narrowed in the middle nor expanded and elevated at its sum- 

 mit, but is sub-triangular in form, and with a fine shallow- 

 channel leading from near its summit near to the anterior 

 ocellus. 



The sides of the propodeum are separated from the poste- 

 rior face by a sharp angle not rounded off nor on the other hand 

 surrounded by carinae as in many species described as Prosopis. 

 This structure is identical w-ith that of typical Hylaeus. 



IS. Hylaeus Fabricius (Latreille emend). 



The species of Europe and ISTorth America described main- 

 ly as Prosopis may perhaps some of them be broken off into 

 separate subgenera but generally speaking, those which I have 

 seen seem congeneric. I have not been able to examine many 

 of the European species, but those which I have do not seem 

 readily separable. Generally speaking the species show little 

 differentiation in the chai-acter of the edeaeiis. More variation 



