CHARLES \V. METZ. 87 



sists entirely of scattered descriptions here and there, with 

 once in a long while a paper dealing with the species of Pro- 

 sopis in a certain locality, or with some small circumscribed 

 group of species. The chief factor, outside of lack of ma- 

 terial, to prevent more complete studies of late, has probably 

 been the great confusion which exists in the descriptions. 

 Because of the published work being so scattered and so 

 often unintelligible, very few if any writers have known just 

 what species had been previously described, and as a result 

 several have been repeatedly redescribed. In other cases 

 where only a few specimens were obtained, distinctions have 

 been based upon merely minor characters, which prove abso- 

 lutely worthless in a large series. All of these conditions 

 taken together make the work of revising the genus unusu- 

 ally diflficult and unsatisfactory. 



The author has endeavored in the present paper to treat 

 all of the North American species, exclusive of Mexican. A 

 systematic treatment of the males has been quite possible, 

 but among the females confusion still exists, and will con- 

 tinue to exist in many cases until some other distinctive 

 characters are discovered. This is especially true of a few 

 species which are widely distributed and exceedingly vari- 

 able. An illustration will be valuable here not only to show 

 the variation which one may expect to find, but also to show 

 the futility of describing, as many writers have done, and 

 are doing, new species based upon minor differences in size, 

 sculpture, or color, and often using for this purpose only one 

 or two specimens. The little species P. cressoni Ckll. is dis- 

 tributed over the whole of North America so far as known, 

 from sea-level to the highest mountains, and thruout its 

 range shows a wonderful series of variations and forms. 

 Some of the variations in the yellow face markings are shown 

 in figures 77-83, and 124-129. In thoracic markings a like 

 variation occurs, extreme southwestern forms having a large 

 amount of yellow on collar, tubercles, and legs, as well as 

 face, while other forms are sometimes entirely dark in the 

 females, except perhaps for a spot on the base of the hind 

 tibiae. In size they vary from the smallest, which are little 



TRANS. AM. ENT. SOC. , XXXVII. 



