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are black and shiny and so situated at the sides of the head as to be half eon- 
cealed by the anterior margin of the thorax. The anterior margin of the orbit 
is extended so as almost to cut the eye into upper and lower sections. The 
portion of the head at the base of the horn, which extends upward directly 
from the clypeus, is very densely pilose or setose, as is also the frontal suleus. 
The occiput has an emargination at each side of the median line; into these fit 
the strong tendons of the powerful muscles which move the head upward. The 
antenne project from the under, outer margin of the head. They are composed 
of 11 segments, the apical 3 of which are laminate; the first is swollen at the 
apex, is as long as the succeeding 7 together, and is very strongly pilose, the 
bristles being on its anterior, external surface (PI. I, fig. 3). The ninth and 
eleventh segments are also pilose at their outer margins and tips; the tenth, 
lying concealed between them, is smooth and blade-like. The small, 4-jointed 
maxillary palpi lie just beneath the insertion of the antenne at each side of the 
labium, which is subquadrate, with the anterior surface strongly swollen. Its 
lateral margins are strongly setose. The maxilla are laminate and hidden be- 
tween the labium and the peculiarly shaped mandibles. They are strongly setose 
on their exterior margins. The 3-jointed labial palpi lie beneath or anterior to 
the maxillary palpi and are attached to the apical part of the lateral margin of 
the labium. 
The most peculiar feature of these insects, which has hitherto been unmen- 
tioned in the literature on the habits of the adult, is the special form and 
function of the mandibles. In the general description of the genus to which 
this insect belongs, the statement is made that “the mandibles are prominent 
and sometimes toothed externally.” In the rhinoceros beetle the external tooth 
of the mandible is curved upward and forward and has the form of the cutting 
edge of a nonconcave gouge. These teeth, one on each side of the head, are by 
their construction and that of the surrounding parts well adapted for chiseling 
out the wood of the tree. (PI. I, fig. 4.) 
The shape and position of the external mandibular teeth, the form of the 
mentum, or chin, which is rounded and curved vertically, and which fits into a 
groove having a like form, in the anterior margin of the prothorax, together with 
the strong, well-attached muscles at the back of the head, prove conclusively that 
the insect, instead of gnawing its way into the tree, chisels into it by an up- 
and-down motion of the head, and it is my belief, for reasons to be given later, 
that no part of the wood is taken into the body. 
The horn of the male is 10 millimeters in length and 4 millimeters in width 
at its base, tapering gradually to 1 millimeter at the tip, which in many speci- 
mens appears as if worn off and repolished. It is sparsely punctured, these 
punctures being fewer toward the tip. 
Thorax.—The pronotum occupies about one-third of the length of the insect 
on the dorsum, is roughly subcircular in general outline, narrower anteriorly, 
having the margins somewhat reflexed. The anterior two-thirds shows a large, 
shallow depression, the surface of which is transversely or concentrically strio- 
punctate, and at the posterior margin of which are two rather inconspicuous 
tubercles, almost coalescing. On each side and in the forward angle of the 
pronotum there is an irregular depression, posterior to which and extending 
narrowly around the posterior margin of the main depression, is another paren- 
thesis-shaped one, broader anteriorly and having its surface roughly rugose. A 
line of submarginal punctures extends around the pronotum. (PI. I, figs. 5 
and 6.) . 
Elytra.—At the base, the wing covers are as wide as the thorax, the surface 
at the outer basal angles being quite smooth. On each elytron are four lines, 
one of which is subsutural, extending from base to apex. The external ones are 
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