50 THE SCOLYTID BEETLES. 



Sculpture. — The dorsal chitinous layer presents many and varied 

 characters of sculpture, the principal elements of which are the 

 striae, including the longitudinal impression and rows of punctures. 

 The interspaces are longitudinal spaces between the striae. The 

 rugosities of the interspaces and striae and the elevated rugose basal 

 margin are all characteristic elements of sculpture. There are ten 

 striae and eleven interspaces. For convenience in referring to the 

 variable characters, these are numbered, beginning with those next to 

 the dorsal suture, when the elytra are closed, or with the posterior or 

 anal margin when the elytra are open. Thus we have interspaces 1 

 to 11, and striae 1 to 10 (figs. 31, 33). 



Interspaces. — In an ideal system (fig. 34) interspaces 1 to 5 are 

 continuous toward the apex with 11 to 7, leaving 6 independent 

 between 5 and 7. The primary tracheae occupy interspaces 1, 3, 5, 7, 

 9, and 11. There is, however, more or less variation and modifica- 

 tion in the elytra of beetles from this ideal arrangement and espe- 

 cially upon the distal ends and their junctions with each other on 

 the declivital area. In Dendroctonus interspace 1 is usually more 

 elevated and continuous to apex, where it joins the very narrow 

 marginal 11; 2 is less elevated to flat, narrowed toward apex, and 

 joins the very narrow and obscure submarginal 10, which becomes 

 broader and distinct toward the base; 3 joins the distinct 9; 4 joins 

 6 around the apex of 5, and also joins 8 around the apex of 7. 



Strise,. — In the ideal arrangement (figs. 1, 31, 34), striae 1 to 5 are 

 continuous with striae 10 to 6, but the usual arrangement on the 

 declivity in this genus is 1 to 3 continuous with 10 to 8, while 4 is 

 continuous with 5, and 6 with 7. The strial punctures range from 

 small to coarse and from very distinct to obscure, and are some- 

 times variable in size and appearance in the same species. The pre- 

 vailing condition, however, of relative obscurity or distinctness in 

 different species is of considerable specific importance. The strial im- 

 pressions also vary within the genus from scarcely to distinctly or 

 deeply impressed, and the prevailing condition within the species is 

 of considerable value. The elytral declivity, as is usual in the scoly- 

 tid beetles, bears some of the more important specific and second- 

 ary sexual characters. 



The other character-bearing areas of the elytra are the lateral, 

 median, and the dorsal toward the vertex and base. 



Vestiture. — The elytra are more or less distinctly clothed with 

 short or long hairs. The length, size, arrangement, and areas occu- 

 pied furnish important taxonomic characters in distinguishing the 

 major and some of the minor divisions, as shown in the synoptic 

 table. A progressive modification m vestiture is from very short 

 hairs over the entire surface to longer hairs and sparsely arranged 



