11 
The head is convex in front and more or less concave posteriorly. 
It presents in the characters of the clypeus and of the occipital and 
frontal ridges, together with the antennie, very valuable characters for 
the separation of genera and species. The difficulty of examining the 
mandibles in dried specimens renders the use of these parts in deserip- 
tions inadvisable, and this holds true also of the maxillee and labium. 
There is also usually a notable variation in structure between the right 
and left mandible. (See fig.2.) The palpi of the maxille and labium, 
the former 6-jointed and the latter 4-jointed, are usually soft and lose 
shape more or less in drying, and are difficult to make out without — 
softening and dissection. The clypeus, if emarginate at the apex, will 
present good differences in the nature of the emargination, whether 
Fie. 1.—Head of Pteronus; I, front; II, rear; III, lateral; and IV, dorsal view: a, ocellar basin; 
b, antennal fovea; c, socket of antenna; d, hypoclypeal plate; e, clypeus; f, labrum; g, vertex; h, 
front; 7, face; j, upper orbit or temple; k, posterior orbit; 1, eye; m, lower orbit or cheek; 7, occiput; 
0, occipital foramen; p, eye; g, cheek; r, mandible; s, occipital fossa; ¢, maxilla; wu, labium; », 
antenna (original), 
broadly or narrowly, deeply or shallowly, and also in the character of 
the lobes produced by this emargination, whether they are rounded or 
triangular, and their width relative to the width of the clypeus. The 
vertex frequently presents very prominent grooves and ridges, and 
these, particularly the ridges surrounding the anterior ocellus and 
inclosing quite a large basin in front of it, are very important. The 
sides of this basin are either strongly and sharply or broadly and 
roundly elevated, or in some genera they are subobsolete or wanting, 
as in Pristiphora. The anterior wall of this basin is usually much more 
strongly raised and wider than the lateral walls, and frequently extends 
beyond the basin nearly to the compound eyes on either side. This I 
have termed in the descriptions the frontal crest. Between the bases 
