HENRY J. FRANKLIN. 405 



eastern Wyoming. Throughout the greater part of its habitat, 

 this species is one of the most abundant of all those present. 



Nests, — I have taken a considerable number of nests of 

 this species. They are usually built in deserted mouse nests 

 on the surface of the ground, being made of the usual material 

 for such nests — dried grass loosely woven together. In these 

 surface nests, I have seldom found more than a few bees. 

 Sometimes, however, their nests are subterranean and, when 

 this is the case, they often contain quite a number of bees. 

 The largest nest of this species which I have ever taken, 

 contained one queen, fifty-three workers and twenty-three 

 males. This nest also contained seventy-eight cells with 

 larvae in them, of which eighteen were queen cells. In this 

 nest, I also discovered the largest single roll of pollen which 

 I have ever found in a bumble-bee nest ; it measured 24 

 mm. in length by 12 mm. in diameter and weighed 3.59 

 grams. All the nests of this species, which I have known 

 about, were in open grassland. 



The male of this species, long known as Psithyrus elatus, 

 has probably caused as much discussion as any bumble-bee 

 in the Western Hemisphere. That it is the true male of penn- 

 sylvanicus, I am able to present the following proofs : 



1. Genitalia. — Its genitalia mark it unquestionably as a true Bonibus 

 instead of a Psithyrus. 



2. Coordination of structure. — The females of pennsylvaniciis and 

 sonorus ^are structurally the same. These males, though differing in 

 color from those of sonorus, are the same in structure. 



3. Concordafwe of habitat. — These males have the same range of 

 habitat as do the females of pennsylvaniciis, and they are taken in cor- 

 responding numbers in the different parts of that range. 



4. Social association. — Whenever these males have been taken in a 

 nest, it has been a nest oi pennsylvanicus females. 



There is nothing about De Geer's original description to 

 make it certain whether his form was the species {^B. ameri- 

 canorum F.) above described, or the one which I am call- 

 ing B. fervidus, or the B. auricomus of Robertson. There has 

 been considerable discussion over the figure which accom- 

 panied the original description, and most of the very recent 

 writers on the group, apparently following Mr. Robertson's 



TRANS. AM. ENT. SOC, XXXVIII. 



