212 AMERICAN HYMENOPTERA. 



an extension of their upper ends. This extension encroaches 

 on the occiput. For this reason, the occiput of Bombias spe- 

 cies is, as a rule, noticeably shorter than that of Psithyriis 

 and the subgenus Bombus. The females of Psithyrus have 

 noticeably shorter eyes than those of any Bombus females of 

 equal size. The eyes of Psithyrus males are also somewhat 

 shorter but not as noticeably so as those of the females. As 

 a rule, a few minute simple hairs may be found scattered 

 over the surface of the eyes. In freshly emerged specimens 

 the eyes are often noticeably hairy, particularly in the males. 

 These hairs are attached between the facets. The eyes are 

 often of nearly the same color as the surrounding integu- 

 ment, but usually they are much lighter and of a color that 

 might, perhaps, be best described as light silvery brown or 

 pale smoky gray. They are also sometimes irregularly 

 mottled more or less. 



Ocelli. — These organs are three in number and are ar- 

 ranged in a curved line on the vertex. Their position in 

 relation to the eye margins and to the supra-orbital line is 

 greatly affected by the amount of extension of the upper ends 

 of the faceted eyes. In some forms {Psithyrus and Bom- 

 bus) they are either tangent to or on the supra-orbital line, 

 and the lateral ones are as far from the eye-margins as 

 they are from each other. In others {Bombias spp.), they 

 are far below the supra-orbital line and the lateral ones, in 

 some males, almost touch the eyes. The ocelli are notice- 

 ably larger in proportion to the size of the individuals, in both 

 females and males of many species of Bombias than they are 

 in any species either of Psithyr7is or of the subgenus Bombtis 

 known to the writer. These organs are sometimes black 

 like the surrounding integument, but usually they are some- 

 what yellowish. They are never as light as the usual color 

 of the faceted eyes. The surface of the integument near 

 them is, for the most part, but slightly punctate. 



Mouth Parts. 

 Of these organs, only the labrum and the mandibles ap- 

 pear to present characters of any value in the determination 

 of species. The other parts will not, therefore, be con- 



