410 AMERICAN HYMENOPTKRA. 



This species is very closely related to B. pennsylv aniens 

 De Geer, but I cannot agree with Herr Handlirsch in believ- 

 ing them to be varieties of the same species. The yellow pile 

 of sonorus is a much deeper yellow than that of pennsylvani- 

 cus, and the scutellum of the female sonorus is much more 

 densely covered with yellow pile than the scutellum of any 

 female specimen of pennsylv aniens which I have ever seen. 

 The differences between the inales of the two species are 

 more striking than are the difiEerences between the females. 

 The third antennal segment of the pennsylv aniens male is 

 slightly longer than the fourth, while the antenna of the ^^- 

 nortis male has these segments practically equal in length ; 

 the differences in the coloration of the pleura, apical dorsal 

 abdominal segments and legs should also be noticed. 



Subgenus BOMBIAS Robertson (genus). 

 ^£7w5/a^ Robertson, Trans. Amer. Ent. Soc, XXIX, 1903, p. 176. 

 " Viereck et als.. Can. Ent., XXXVI, 1904, p. 97. 



Viereck, Trans. Amer. Ent. Soc, XXXII, 1906, pp. 224 and 

 240. 

 " Swenk, Ent. News, XVIII, 1907, p. 294. 

 Subgenus Bombias Franklin, Trans. Amer. Ent. Soc, XXXVII, 1911, 

 p. 161. 



Type. — Bovtbns {Bombias) aurieormis Robertson. 



Robertson took certain species from the genus Bombus, as 

 formerly recognized, and placed them in a separate genus, 

 Bombias. He distinguished the females of the two genera, 

 thus recognized by him, from each other entirely by means 

 of the size and position of their ocelli. He distinguished the 

 males by the difference in the size and position of the ocelli, 

 the difference in the size of the eyes, the difference in the 

 length of the malar space and the difference in the relative 

 lengths of the basal segments of the flagellum of the antenna. 

 The study of a large number of species has shown, however, 

 that these differences are not constant. Certain of the B0771- 

 bias species, which the writer has placed in the Fraternus 

 group, grade up so closely to certain species of the Dum- 

 oucheli group of the subgenus Bombtis that they could almost 

 be included in that group. It is found, furthermore, that 



