250 RHYNCHOPHORA. 
of the prothorax and the cylindrical part of the elytra are either shining, or subopaque 
and alutaceous, owing to the presence of microscopic reticulation, and are usually 
feebly punctured with minute points, sometimes scarcely discernible with a low- 
power magnifier, without trace of impressed striz. Pubescence and hairs are absent, 
except at the extremities of the body. 
These features of surface-structure, which give the insects a peculiar smooth look, 
are common among, and almost confined to, the ambrosia-feeding Scolytid, but are 
most marked in this subgroup. 
The declivity and extremities of the elytra show great variety in form and armature, 
and are singularly developed in Amphicranus. 
The prosternum is variable in length, depending on the greater or less elongation 
of the species; the intercoxal process is indistinct or wholly absent. 
Although many Corthyli are black or dull brown, there is among them a somewhat 
greater range of colour and marking than is usual in the Tomicides. Differences 
between the colours of the prothorax and elytra and a tendency towards decoration of 
a testaceous surface with patches or clouding of a darker shade are met with, and 
form a welcome relief from the dull uniformity prevalent in the bark-feeding 
Tomicides; and in two or three species of Amphicranus, elegance of form and effective, 
if simple, coloration are attained. 
The division of the subgroup into genera, with their diagnosis, is not altogether an 
easy task. The variety of structure, particularly in the antennee, is unusually great 
aud a temptation to multiply genera undesirably. These most interesting insects 
have been little collected; their sexual differences are often considerable, and in few 
species are both sexes known. The genera tend to inosculate, and characters, usually 
trustworthy, are not always constant throughout the members of what must be 
regarded as a genus. 
The classification of the Corthyli can only be put on a sound and permanent 
basis by the investigation of further material collected with special regard to the 
representation of both sexes. 
Some fifty species, of which all but six are new, are here described or recorded 
from Central America, and of these thirty-four have reached us in single specimens. 
Such a collection gives little idea of the number of forms that must exist in the forests 
of the American tropics. 
Our species are grouped into seven genera, of which three are new. Eichhoff 
recognized eight genera, but two of his, Anchonocerus and Phthorius, have not been 
' found in our region, and two others, Zrypocranus and Steganocranus, both imperfectly 
diagnosed, are also not found or are represented by forms here included in Pterocyclon 
and Amphicranus respectively. 
In the year 1867, Ferrari, in his ‘Die Forst- und Baumzuchtschadlichen Borken- 
kafer (Tomicides, Lac.), described at length the Corthyli collected by Moritz in 
