1896.] NATURAL SCIENCES OF PHILADELPHIA. 27 



with flower-studies undertaken in botany, the relations between bees 

 and flowers being among the most fascinating phenomena in natural 

 history. 



The present essay on Perdita is the first step toward the realiza- 

 tion of the above mentioned ideal. Imperfect as it undoubtedly is, 

 it has grown like a mushroom under the hands of the writer ; so 

 that the probability of finishing the whole series of bee-genera seems 

 remote indeed, if each is to increase in a similar fiish ion. Seventeen 

 North American species of Perdita were known before the writer 

 began to study them ; of these, two are not considered valid, but 55 

 have been added, bringing the list up to seventy ! Thus, in number 

 of species described, Perdita becomes at a bound the largest of North 

 American bee genera. 



MATERIAL EXAMINED. 



By far the greater part of the material studied has been collected 

 by the writer in New Mexico. With great kindness, Mr. AY. J. Fox 

 loaned a series of specimens containing his Lower Californian types, 

 and all the species of Cresson except cephalotes, as well as several 

 herein described as new. In various other ways, such as comparing 

 types, Mr. Fox has throughout the whole investigation given 

 invaluable assistance. Mr. C. F. Baker was so good as to send me 

 the specimens he and his wife had collected in Colorado, which 

 included some new forms. Mr. C. Robertson has given some 

 very valuable information regarding the habits of the two eastern 

 species. Some interesting species have been found by students of 

 the college. Miss Mae Gilmore, Miss J. E. Casad, Mr. Alfred Holt 

 and Mr. C. Rhodes, as duly indicated below. My botanical col- 

 league, Professor Wooton, found one new species. 



The writer has seen all the species treated of, except cephalotes, 

 halictulus and bicolor. Of the 70 species, 26 are known in both 

 sexes, 26 only in the ^ , 18 only iu the 9 . 23 are at present only 

 known from uniques. The flower-visiting habits of 50 species are 

 known. The nesting habits are as yet unknown. 



CHARACTERS USED. 



It is hoped that those who may have occasion hereafter to describe 

 species of Perdita will read this section, as a study of the published 

 descriptions shows that some important characters are almost always 

 omitted. 



