J. C. HUTSON 207 



and always less than the ocello-ocular line. The exact propor- 

 tions vary with the species. The surface between the ocelli, or 

 intraocellar area, is slightly raised and each of the ocelli has a 

 slight depression at its outer base. 



Vertex. — Behind the ocelli is a shallow oblong depression, and 

 posterior to this there may be a raised oval area, which might be 

 regarded as the vertex proper, but in this paper the vertex is 

 considered that part of the head bounded anteriorly by a line 

 through the lateral ocelli, posteriorly by the occipital ridge and 

 laterally by the genae and tops of eyes. 



Occiput. — The occiput is the narrow circular strip at the back 

 of the head surrounding the occipital foramen. It is of no sys- 

 tematic importance. 



Genae. — The cheeks or genae are paired sclerites at the back 

 of the head between the compound eyes and the occiput, and 

 extend from the vertex to the base of the mandibles. They are 

 narrowest at the top and gradually widen ventrally, where they 

 curve in on each side to meet between the occiput and the gular 

 cavity, and extend laterally outwards under the eyes to meet the 

 clypeal extensions. 



The mouth parts with the exception of the mandibles do not 

 appear to be of systematic importance, but mention may be made 

 of the labrum, which is a narrow oblong strip attached under the 

 lower edge of the clypeus. In pinned specimens it is usually 

 hidden behind the closed mandibles, but if these are opened the 

 labrum can be seen as a flap lying over the other mouth parts. 



Mandibles. — The mandibles of females are long, rather curved, 

 bluntly rounded at the tip, and may or may not have a tooth on 

 the inner side according to the species. In males they are shorter 

 and taper to a point. 



The extension of the lower angle of the clypeus meets a cor- 

 responding extension of the genae and the two together furnish 

 articulations for the mandible in the following manner. On the 

 under part of the clypeal extension is a condyle which fits into a 

 socket on the upper side of the mandible, while the genal piece has 

 a facet to receive the condyle on the lower side of the mandible. 

 There is also a median basal projection on the outer side of the 

 mandible, serving as an attachment for nuiscles. This projection 



TRANS. AM. ENT. SOC, XLV. 



