AIDS IN CLASSIFICATION. 33 



any other single character. lu almost all beetles of considerable size, 

 that is, more than a quarter of an inch in lengtb, 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 

 the club-horned tribe, (ClavicornesJ and" the short-winged tribe, 

 (Braclielytra.) 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 LathridiidiB, Trichopterygida>, and Pselaphida?, 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 anteunie. 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 Cleridse. Some of the short- winged 

 scavengers {StaphijUnidie), with an irregular number of tarsal joints, 



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