280 
GEO. II. HORN, M. D. 
This structure has been well described by Mr. Waterhouse. When 
the tip of the prosternuni is closely applied to the metasternum, the 
portion of the ape.x not concealed assumes various forms, being tri- 
angular, rounded, truncate or dilated (see muticus and species near). 
For convenience of expression in the analytical table, the visible free 
portion has been assumed to be the tip, and is so spoken of in the 
table. 
SciTTEEEUM. — The two forms observed are charactei’ized by the 
presence or absence of a transverse carina. This structure seems to 
have been considered as invariable as the angular carina of tli,e 
thorax, but in several of our species the carina may be distinctly 
jiresent in some specimens and entirely absent in others. 
Elytra. — In nearly all of our species the sides of the elytra are 
slightly sinuate behind the humeri, and then more or less dilated 
before finally narrowing to the aj)ex (PI. viii, fig. 7), but in many 
others the elytra narrow from the luuneri to the apex almost without 
sinuation as in difficilis (PI. viii, fig. 8). In the former case the sides 
of the abdomen are much less visible from above than in the latter. 
As a rule the elytra are narrower in the male. The disc is not often 
costate and then only in the species of the tropical ty[ie, as in Couesii, 
cavatns and macer, but in very many species there is on each elytron 
a very vaguely indicated costa. 
The surface sculpture is practically the same in type in all our 
species, and is derived from a form described as imbricated, resem- 
bling, when magnified, a series of pointed tiles, closely placed, in 
which the points are somewhat elevated. The sculpture in s’ome 
species might be described as closely mucronate. 
The apices of the elytra are not, in any of our species, provided 
with the curious prolongations and modifications seen in the tropical 
forms. The tip is rarely very acute {nevadensis) , usually rounded. 
The edge is usually serrulate, and in a few species entirely sim[)le 
(jmdicus, etc.). 
PvGiDiUM. — In very nearly all our species the pygidium is pro- 
vided with a median smooth or elevated line, in many species forming 
(piite a ridge, and in a good number the ridge is ])rolonged, forming 
a spine sometimes emarginate at its apex {macer). The presence or 
absence of the prolongation is one of the most constant of the struc- 
tural characters, although specimens of rnficolUs are occasionally 
seen without it. The pvgidium oi pulchellm is acute at tip, the carina 
well marked, but not independently projecting. 
