NORTH AMERICAN BUPRESTID BEETLES 7 



touching each other. Some of the species have the inner portions of 

 the claws only feebly turned inward, and these are placed in the key 

 with those species having the claws simply cleft. In making use of 

 this character in the key, the claw? on the anterior feet should be 

 used, as the claws sometimes not only differ in the two sexes, but 

 also in the three pairs of feet, especially in the males. 



Genitalia. — The male genitalia are strongly chitinous, and consist 

 of the lateral and median lobes. They differ from the genitalia in 

 the family Elateridae by having the basal piece and lateral lobes con- 

 solidated, and by the coadaptation between the lateral and median 

 lobes to allow the median lobe to be extended beyond the tips of the 

 lateral lobes. The genitalia show considerable differences in shape 

 and sculpture, sometimes in the most closely allied species, but show 

 scarcely any variation in the species. It it a very useful character 

 for separating the species, and especially in checking up individual 

 specimens that are more or less abnormal. 



The genus Agrilus as a whole, is a newer, more plastic group 

 of the Buprestidae, with structural characters unsettled, and many 

 species in a process of evolution. The species of this genus have 

 probably developed at a more recent date, for so far as known, none 

 of them live in conifers, which are of earlier origin than the de- 

 ciduous trees. Biologically our species can be placed into three 

 groups as follows. 



First. — Many of our species are well established and scarcely any 

 variations can be found in their structural characters. These species 

 can be easily distinguished, the genitalia of the male are quite dif- 

 ferent, therefore, not permitting their interbreeding, the species as 

 a rule confine their habits to a single genus or closely allied genera 

 of host plants, and scarcely any intermediate forms are found. 



Second. — In some species such as egenus, otiosus, etc., the females 

 are not distinguishable on structural characters, although the males 

 as a rule are easily separated on secondary, external sexual char- 

 acters, the male genitalia show considerable differences similar to 

 those in the first group, and the species usually confine their habits 

 to a single host plant. 



Third. — This group is composed of species such as politics, arcuatus, 

 etc., which are at present in a high state of evolution, and must be 

 considered as composed of a number of phytophagic species. These 

 phytophagic species can not be separated on any structural char- 

 acters, and the genitalia of the males are almost identical, which 

 will permit interbreeding between the different forms, but the species 

 have become capable of living only in one genus or species of plants, 

 which consequently they select. In this group a number of inter- 

 mediate forms can be expected, as some adults may accidentally 

 select a new host plant and continue to breed in that plant. 



