31 



the strongly convex pronotum so as to be invisible from above in the Ipince and 

 Micracince. It bears many of the most important characters used in classifi- 

 cation. 



The mouthparts are only rarely made use of in the keys given in this paper, 

 and need not be described in detail. The labrum is absent. The mandibles 

 are powerfully constructed, without peculiar characters. The maxillae and 

 labium, on the other hand, present excellent constant and peculiar characters, 

 some of which have been used in classification by earlier writers. The objection 



J>is. 



Prothorax fleso- Jfetathorajc 

 thorax 



Hea.d Thorax AVdomen, 3 risible sejs. 



FIG. 2. HYLXTBGOPB PINIFEX FITCH; SIDE VIEW. ORIGINAL. 



Ant., antenna; EL, elytron, showing striae; El. dec., elytral declivity; Epis., epistoma; F. ex., 

 fore coxa; Fr. front; Gen., gena; H. ex., hind coxa; M. ex., middle coxa; Md., mandible; M. epim., 

 mesepimeron; M. epist., mesepisternum; Met. st., metasternum; Metepist., metepisternum; Mst., 

 mesosternum; MX., maxilla; Pn., pronotum; P.m. st., process of the mesosternum; Scut., scutellum; 

 Sut. st., sutural stria. 



to their general use applies to most internal structures ; that they can be examined 

 only after careful dissection requiring a microscope and a certain skill in mani- 

 pulation. The characters of the maxillse include the relations of the sclerites 

 and the structure and arrangement of the setae. The lobe is spinose in most 

 species, but fringed with long slender hairs in ambrosia-beetle genera. The 

 labium is deserving of more attention than it has yet received in literature, 

 and if it were not for the difficulty in examination, would be used freely in 

 these keys. The mentum, ligula, and palps bear excellent generic and specific 

 characters. 



The eyes are feebly convex, usually elongate-oval, with the margin entire 

 or with the front margin more or less deeply emarginate. In the genera Trypo- 

 dendron, Xyloterinus, and Polygraphus, the eyes are completely divided by 

 the median emargination (PL 9, fig. 36). Polygraphus is otherwise very 

 widely separated from these other two genera, and the condition of the eyes 

 is an excellent example of convergence. 



The antennas are geniculate, with a well developed scape, funicle, and a 

 prominent club. The latter may be regularly segmented with transverse or 



