184 RHYNCHOPHORA. 
on a few points, such as the association of Xyleborus and Gnathotrichus, and the 
unnecessary separation of the Amphicranid from the Corthylid genera. Eichhoff’s 
subgroups, or, as he calls them, subfamilies, are somewhat vaguely defined, and are 
arranged by him in two main sections, Phloeophagi (op. cit. p. 72) and Xylophagi 
(op. cit. p. 308). Apart from the bark or wood-boring habits which the names indicate, 
the components of each section are to be distinguished by the structure of the maxille, 
which in the first-named are set internally with stout radiating spines and have the 
apical joint of the palpus non-striate, and in the second are set with slender seta, 
closer apically, and have the apical joint of the palpus striate. In the Xylophagi the 
sutural stria of the elytra is weakly impressed or absent. 
Leconte and Horn justly point out (Class. Col. N. Am. p. 517) that these oral 
characters are very difficult to observe and verify. ‘To do so exacts, indeed, the 
laborious and troublesome operation of dissecting out the maxille and mounting them 
in balsam. When this is done, the distinctions are found to be real and important, if 
not quite so decisive as Kichhoff supposed ; the striation of the palpus at least is little 
evident to me except in the Corthyli, where it is very marked. It is reasonable to 
suppose that the structure of the buccal organs is adaptive and correlated with the 
assumption of wood-boring habits; and it may be inferred that these habits have been 
independently acquired by various Tomicid forms. This possibility will scarcely be 
contested by anyone who is familiar with the variations existing in the boring-habits of 
Scolytide. But if such be the case, the modifications in maxillary structure will be of 
secondary and subordinate value, and not a feature on which to base the primary 
division of the group. 
In the following table the group of Central-American Tomicides is divided according 
to the subgroups established by Hichhoff, except when the association seems to be 
incorrect. 
Thus Gnathotrichus, which appears to stand midway between Pityophthorus and the 
Corthyli, is placed with the Pityophthori, following Leconte, rather than with the 
Xylebori, and the Corthyli and Amphicrani are brought together under the former 
name. 
The order in which these subgroups are diagnosed and will be described is 
approximately that employed by Leconte, and brings together the Pityophthori and 
Corthyli. It has the disadvantage, however, of separating the former from the Tomici, 
which approach them very closely, the distinctions between these two subgroups being 
in many cases slight and of doubtful value. 
Club tunicate or subtunicate, obliquely truncate, the upper surface principally 
corneous, the lower surface, to which the sutures are mainly limited, spongy 
at the tip. Tuibiz stout, more or less strongly serrate; at least the anterior 
tarsi retractile. 
