NORTH AMERICAN COLEOPTERA. 67 



are uniques. In the fifty species enumerated both sexes are described 

 of forty-two, seven are known only by females, one by the male. 



Having an unequaled oppoilunity in both the quality and quan- 

 tity of material, it remains to be seen whether the results of my study, 

 as given in the following pages, will make a really difficult subject 

 comprehensible to others. 



The genus as recognized in the following pages is in full accord 

 with those who unite Chrysobothris and Colobogaster, the reasons for 

 which have been aptly given by James Thomson, in " Typi Bupres- 

 tidarum," App. 1, p. 40, and need not be repeated here further than 

 to say that the size of the cavities for the articulation of the antennae 

 is very variable in our species. The first joint of the hind tarsi is 

 always as long as the next three, frequently much longer. 



The general form of the species is variable, but the variation is 

 not as great as in some genera, such as Psiloptera, which are truly 

 lX)lymorijhic: For a better idea than can be given by description 

 the reader is referred to the annexed sketches. 



In the various synoptic tables some of the characters used are 

 common to both sexes, others are purely sexual. In the first cate- 

 gory are those found in the surface of the thorax, the anterior mar- 

 gin of prosternum, the last ventral segment, and finally the clypeus. 



The disc of the thorax may be regular and even, more or less 

 equally punctured and without either grooves or irregular elevations, 

 this is illustrated in the first six species on Plate ii and others on 

 Plates vi-vii. The irregular disc, that is with grooves or irregular 

 callosities and with usually uneven punctuation, is by far the most 

 abundant form, and, in our fauna, more characteristic of the genus, 

 see Plates iii and iv. 



The anterior margin of the prosternum may be lobed or truncate, 

 neither character being ])eculiar to any of the groups into which I 

 have divided our species. The truncate prosternum occurs in den- 

 tipe^, trinervia and the related species as well as elsewhere, the form 

 is illustrated by diagram fig. 98. In those species in which the pros- 

 ternum is lobed in front, the lobe varies greatly in form and size — 

 from a simple arcuation of the middle of the front margin (fig. 99) 

 to an abrupt, well developed projection (fig. 22). 



