AIDS IN CLASSIFICATION. 
33 
any other single character. In almost all beetles of considerable size, 
that is, more than a quarter of an inch in length, this character is very 
uniform, or, in other words, the number of tarsal joints in the insects of 
any one section or family, is remarkably unexceptional. It also has the 
advantage, in insects of this size, of being easily determined, if not by 
the naked eye, at least by the aid of a simple lens. 
But the insects which are necessarily the most difficult to examine 
and classify are the very small ones, and here the character founded 
upon the number of tarsal joints not only becomes more difficult to de- 
termine, but more exceptional, and therefore of less value. We there- 
fore give the following suggestions to aid the inexperienced student in 
cases of this kind. 
The principal difficulty occurs with respect to numerous families con- 
taining very small species in the first or pentamerous section ; and 
these are mostly limited to what are known as scavenger beetles, both 1 
the club-horned tribe, (Clavicornes,) and the short-winged tribe, 
(Brachelytra.) In the minute species of both of these tribes the number 
of tarsal joints is very irregular, one of them being often indistinct or 
wanting, especially in the posterior feet ; and in three families at least, 
the Lathridiidse, Tricliopterygidse and Pselaphidse, two joints are want- 
ing in all the feet, making them apparently but three-jointed. 
The student will naturally inquire, why place these insects in the 
pentamerous section? The answer is, that they harmonize more closely 
with the insects of this section in their other characters, whilst they do 
not affiliate with the insects of the other sections which agree with them 
in the number of tarsal joints. An examination of their other charac- 
ters will usually enable the student, after a little experience, to refer 
these insects to their true position ; though cases sometimes occur which 
puzzle the most astute entomologist. They can hardly be confounded 
with the Heteromera, because these are, for the most part, much larger 
insects, and the exceptionally small species belong mostly to the tribe 
of Trachelides, which are distinguished from these and most other 
beetles by having the head attached to the thorax by a narrow neck. 
They differ from the Tetramera in the form of the tarsi and also that of 
the antenme. Almost all these small species with deficient tarsal joints 
have these parts slender and simple, whilst all the genuine Tetramera 
have the tarsal joints somewhat widened and covered beneath with a 
dense brush of short hair, and the last joint but one is wider than the 
others, and divided into two lobes, between which the last joint is in- 
serted. The only pentamerous beetles which have some of their tarsal 
joints obsolete, and at the same time have the last joint but one bilobed, 
are a part of the serricorn family of Clerhhe. Some of the short-winged 
scavengers (Staphylinidw), with an irregular number of tarsal joints, 
