292 A. L. MELANDER. 



Until some experience is gained, the assignment of species to the 

 various groups given by Mr. Fox will often be confusing. Owing 

 to the strenuous way in which the females use their mandibles, the 

 teeth are frequently worn down or quite wanting in old specimens. 

 In these cases care should be noted before a final decision is given 

 that the specimen is a new species in an incongruous group. The 

 differences given on page 221 of Mr. Fox's paper for separating the 

 groups imperialis and anthophorce are inversely stated, and should 

 read thus : 



First abdominal segment ( 9 ) smaller than second, more or less nodose ; in % the 

 first and second segments are not similarly sculptured, the first coarser 

 than the second Gr. imperialis. 



First and second segments ( 9 ) sessile; first segment % not more coarsely sculp- 

 tured than second Gr. anthophorx. 



Pygidial structure is sometimes variable within a species, and 

 hence, although generally a good character, cannot be regarded as 

 infallible. In similima, for example, the striae are not uniform, 

 tending to diverge at the tip. Hippoclamia seems to represent the 

 extreme where the stria? have become transverse, and since as yet no 

 intermediate gradations have been discovered, this form can be 

 given specific rank. The structure .of the petiole of the abdomen, 

 the vestiture and sculpture of the body, in fact every single charac- 

 ter that can be chosen is subject to greater or less variation. An 

 interesting character which appears to have been unnoticed hereto- 

 fore is the peculiar plumose structure of the hairs covering the body 

 of certain of the Photopsis males. This is often especially notice 

 able on the abdominal fringes, and recalls the vestiture of the Bees. 



In conclusion, I wish to thank the following individuals and insti- 

 tutions who have generously loaned their collections for unlimited 

 study: Rev. G. Birkman, of Fedor, Texas; Mr. Samuel Henshaw, 

 for the Museum of Comparative Zoology, Cambridge, Mass. ; Mr. 

 Theo. D. A. Cockerell, for unworked material of his own and 

 belonging to the New Mexico Agricultural College, Mesilla ; Mr. 

 C. F. Baker, for the Chicago Academy of Sciences; Dr. O. S. 

 Westcott, <>f Chicago; and my collaborator, Mr. C. T. Brues, of 

 New York. The types of most of the new species are located in 

 the collections of these gentlemen as indicated at the end of each 

 description. 



