KEY TO THE BUMBLE-BEES. 



The following key is to the species of the Atlantic Coast 

 of the United States. The more western and extremely 

 variable rufocinctus is omitted. P. stands for Psithyrus; 

 B. for Bombus; and B.B. for Bombias, a subgenus of 

 Bombus. "Occiput" is the top of the head. "Pleura" 

 refers to the side of the thorax especially in front, below 

 the front wings. "Scutellum" is the triangular hind 

 part of the top of the thorax. * "Interalar band" is on the 

 top of the thorax, between the wings. The "malar 

 space" is between the eyes and the jaws. The "supra- 

 orbital line" is an imaginary line from the top of one com- 

 pound eye to the top of the other. The notes on color 

 refer to the color of the hairs, not to the chitin; and the 

 upper side of the abdomen is all that is considered when 

 giving its color. 



1. Divisions of tarsal claws very unequal; 12 antennal 

 joints; 6 visible, abdominal segments (Females) 2. 



Divisions of tarsal claws subequal; 13 antennal joints; 

 7 visible, abdominal segments (Males) 15. 



Females 



(The female of P. tricolor is unknown unless fernaldce 

 be it.) 



2. Outer face of hind tibiae convex and hairy. Psithyrus. 3. 

 Outer face of hind tibiae concave and bare, except at 



margins. Bombus 5. 



3. Occiput black with little or no yellow; lower portion 

 of pleura with dark hairs P. ashtoni. 



Occiput with much yellow 4. 



4. Thorax without interalar, black hairs but disk bare; 

 pleura light; little or no yellow on fourth abdominal seg- 

 ment; face largely dark P. laboriosus. 



Thorax with interalar, black hairs; pleura mostly 

 light; no reddish on fifth abdominal segment but yellow, 

 at least on the sides, on the fourth P. insularis. 



Thorax with or without interalar, black hairs; lower 

 pleura yellow or dark; fourth abdominal segment almost 

 entirely covered with yellow r ; often with reddish on sides 

 of fifth; apical, abdominal segment very pointed and 



strongly recurved P. fernalda. 



29 449 



