AMERICAN COLEOPTERA. 183 



Sierra Nevada forms, sequoiarum, Edwardsii, intermedius and Hornii, all seem to 

 rue to be geographic races of sequoiarum aud closely related to Audouhii. Finally, 

 in the most southern part of the range, the greatest divergence from the northern 

 Audouiui, Omus Imvis is reached. 



The purpose of this plate is to present, more clearly than by words alone, the 

 remarkable fact that each of the species of Omus is confined to its own especial 

 territory, as may be seen by following the dotted lines which outline the regions 

 in which each is found. 



PLATE II. 



The drawings of the labrum of several species are given to show the variation 

 in this part of the body. They are drawn from individual specimens, and it 

 should be remembered that the labrum is subject to considerable individual 

 variation. 



The mandible of the usual form, both front view and side view, is drawn to 

 show the differences that exist in the mandibles of dorsalis, hamata aud marginata. 

 The front view is not drawn for these, as it is the same as the normal view. 



The apex of the elytra, % and 9 > is drawn for several species, but not for all 

 those iu which the apex is externally emarginate. 



To avoid any misunderstanding of the terms used in describing the maculation 

 of the elytra, the different marks are numbered, and a corresponding number is 

 given in the key iu the lower right hand corner. 



PLATES III AND IV. 



In these plates the markings of most of the species are shown. When the 

 markings vary a specimen with the most complete markings has been selected, 

 and departures from the types shown will usually be in the direction of the 

 obliteration of the markings, e.g., in sexgnttata, the drawing shows four dots, 

 though this species often occurs with three or two or one, or even none at all. 

 In some of the drawings, the elytra are wider than they should be. The draw- 

 ings are all about twice the natural size. 



TRANS. AM. ENT. SOC, XXVIII. JUNE, 1902. 



