HENRY J. FRANKLIN. 209 



The vertex is considered as extending from the occiput 

 half-way down to the supra-antennal line (the line tangential 

 to the upper sides of the antennal attachments). While the 

 occiput appears to provide no good classification characters 

 aside from its varying length and the color of its pile, the 

 variable position of the ocelli on the vertex of all castes is 

 of much assistance in marking the limits of certain groups 

 of species which have been, in this paper, placed together in 

 the subgenus Boinbias for reasons given in another place. 

 This character is also useful, to a considerable extent, in the 

 separation of the different species of these groups. With 

 the males of the Bonibias species, the vertex is usually more 

 or less narrowed toward the occiput. The frons extends 

 from the vertex to the clypeus and also, in triangular exten- 

 sions, down on each side of the clypeus to the malar space. 

 A median groove extends from the middle ocellus down to the 

 upper portion of the frons. There is a short carina between 

 the a.ntennal insertions. Aside from the color of its pile, the 

 frons appears to be without value in classifying species. The 

 clypeus is a trapeziform plate occupying the lower portion 

 of the front of the head. It is marked off from the frons by 

 quite strong sutures. It's surface is rather strongly convex 

 and the labrum is attached to its lower margin. This plate 

 is of some taxonomic value as its punctation varies greatly 

 between different species, though it is apparently very con- 

 stant within species and sex limits. The clypeus of the 

 males is usually well covered with hair, while that of the 

 females, in Bombus at least, is mostly naked. The compara- 

 tively smooth and hairless area between the lower end of 

 the eye and the base of the mandible, on each side of the 

 head is, in this paper, called the " malar space." This region 

 is probably made up partly from an extension of the frons 

 and partly from a forward extension of the gena. It varies 

 greatly in length between different species and is of much 

 taxomomic value. The sides of the head, behind the eyes, 

 are known as the cheeks or gense. There is no line of 

 demarcation between the genae and the occiput, the mutual 

 limits of these plates being indefinite. The cheeks are 



TRANS. AM. ENT. SOC, XXXVIII. (27) 



