CHARLES W. METZ. 91 



half of these will stand. In the present work it has been 

 possible to recognize about twenty species as certainly dis- 

 tinct, and ten or twelve more, as yet but little known, which 

 may be distinct. A number of the species, however, were 

 originally described from females that have since been asso- 

 ciated with the males, so about half of the species originally 

 described from males are probably valid. 



The association of the sexes in Prosopis is extremely dif- 

 ficvilt, indeed practically impossible in some cases, unless the 

 specimens are actually taken in copula or reared. In the 

 males as a rule an entirely different set of characters is 

 used for identification than is used in the females, and oc- 

 casionally the two sexes are so entirely different in general 

 appearance that they cannot be certainly associated with our 

 present knowledge. The proportions of the parts of the 

 face, altho of great value in determining species in each sex, 

 are of little use in associating the sexes. In face markings 

 the sexes never agree, altho they often show the same ten- 

 dency ; and in thoracic markings they may or may not agree, 

 altho here also the same tendency toward a large or small 

 amount of color is observed. In sculptural characters a 

 greater constancy is found, and often the sexes can be de- 

 termined with a considerable degree of accuracy in this way. 

 In actual practice all these characters must be taken into 

 consideration in associating the sexes, and also the locality 

 records must be considered. Many of the species can be as- 

 sociated with a fair degree of accuracy in the latter way if a 

 large series is obtained. 



Not only is it often very hard to associate the females with 

 the males, but in some cases it is very hard to separate the 

 females of nearly related species among the wide range of 

 varieties. In this sex the entire group is extremely uni- 

 form, and is lacking in those characters which distinguish 

 the males. The face marks are less pronounced and less 

 constant than in the males, and the swollen scape of some 

 of the latter is not found at all in these. Consequently in 

 species having closely allied males, the females are usually 

 so near alike or intergrade so much that accurate separation 



TRANS. AM. ENT. SOC, XXX VII. 



