44 PROCEEDINGS OF THE ACADEMY OF [1896. 



ers, the whole matter seems clear. Yet it must be confessed that on 

 Verbesina the yellow beata is extremely rare, while the dark verbe- 

 since abounds. 



The face-markings, so distinctive of species, differ greatly as a 

 rule in the sexes, and in most species are very constant. There is 

 every probability that they serve as recognition marks ; and it is 

 here significant that when they are very variable, as in 9 zebrata, 

 there is no other species of Perdita on the same flowers that could 

 be confused with the varying one. 



The species appear to be all single brooded, but the great resem- 

 blance between the vernal numerata and the late summer bigelovice, 

 suggested the possibility of double-brooded seasonally dimojphic 

 species. The strongest fact, however, that militates against this 

 idea is that there are so many more late summer and autumn spe- 

 cies than vernal ones, while the eastern odomaculata is represented 

 by no congener at all in the spring. 



Another question arose as to the possibility of dimorphism in the 

 males of some species ; references to this matter, which deserves 

 further study, will be found under the species concerned. 



It will be observed that the grouping of the species is arbitary, 

 those being associated which the student is likely to meet with on 

 the same flowers, or in the same part of the country. This was done 

 because it was felt that no natural arrangement could yet be arrived 

 at, and a purely artificial one, based solely on considerations of con- 

 venience, was better than one which might give a false idea of rela- 

 tionships. The difficulty arises in many cases from the so-called 

 " kaleidoscopic " characters, the possession of which by two species 

 does not necessarily imply descent from an ancestor exhibiting them. 

 Thus hiteola and beata are colored alike in almost every detail 

 (except the black on the pleura of beata), and are extremely diflfer- 

 ent from any other Perdita. But beata in its size and hairy meso- 

 thorax approaches the albipeunis group and departs widely from 

 hdeola. The character of armed cheeks has already been referred 

 to, and several others might be cited. How strangely the several 

 "specific" characters may appear or disappear, is shown well in the 

 series of alblpennis and verbesince. 



There is, however, one natural group, that of texana and latioVy 

 which is very distinct and may ultimately be regarded as forming 

 a distinct genus. F. Smith's generic name Macrotera has been used 

 for texana, but perhaps incorrectly. 



