THE GENUS DENDROCTONUS. ( 
has three to four closely connected joints denned by curved lines. 
The front of the head has a distinct middle elevation toward the 
base of the mandibles, called the epistomal process (see figs. 2, 3). 
The pronotum is slightly more than half to slightly less than half 
as long as the elytra, which have fine to coarse rugosities between 
rows of obscure to distinct punctures. 
The diagram, Plate I, gives the technical and common names of 
the beetles of the genus, and shows how the different species fall into 
natural primary and minor divisions according to certain structural 
characters and peculiar habits. 
ADULT CHARACTERS. 
In the species of Division I the pronotum is somewhat elongate and 
as broad as the elytra, and in those of Division II the pronotum is 
shorter and is usually narrower than the elytra. 
In species 1 to 8 (subdivision A) the body is somewhat slender, 
and the pronotum is but slightly narrowed toward the head, which 
in all but species 3 (comprising subsection b 1 ) has a frontal groove 
and two frontal elevations. In species 1 and 2 (section a 1 ) the elytra 
are without long hairs, while in species 3 to 8 (section a?) there are 
long hairs toward and on the declivity. 
In species 9 to 11 (subdivision B) the body is stouter and the 
pronotum is distinctly narrowed toward the head, which is without 
frontal groove or elevations. In species 9 and 10 the punctures of 
the pronotum are moderately coarse and deep, while in species 11 
they are shallow and usually fine, with the surface more shining. 
In species 12 to 21 (subdivision C) the punctures of the pronotum 
are of irregular size, while in species 22 and 23 (subdivision D) 
they are regular. 
In species 12 and 13 (section a 3 ) the striae of the elytral declivity 
are deeply impressed, and the interspaces are convex, while in 
species 14 to 21 (section a 4 ) the striae are but slightly or not at all 
impressed and the interspaces are flat or but slightly convex. In 
species 14 to 19 the striae of the elytral declivity have obscure to 
fine punctures, while in species 20 and 21 the strial punctures are 
coarse and distinct. Species 22 and 23 are easily distinguished by 
their large size, evenly punctured pronotum, which is subelongate and 
almost as broad as the elytra, and by the very large and prominent 
head. 
EXTERNAL SEXUAL CHARACTERS. 
In species 1 to 8 (subdivision A) the females are distinguished by 
a transverse, rather broad, elevated ridge across the pronotum near 
the anterior margin, moderately broad head, and moderately large 
mandibles. The males are without the transverse ridge across the 
