28 



THE SCOLYTID BEETLES. 



Poststernellar area — The poststernellar area is well defined and 

 serves to completely inclose the coxal cavity. It has been referred 

 to as the epimeron, but since the epimeral is so clearly defined as a 

 lateral area, it appears to more correctly represent the poststernellum, 

 which in the mesosternum and metasternum is not evident, or is 

 modified to accommodate the large coxal cavities. 



THE MESOTHORAX. 



The mesothorax (figs. 18, 19) is short and partially hidden 

 from view by the prothorax, which covers the anterior third of the 

 sterna, pleurites, and tergites, while the base of the elytra covers 



Tergites 



Wing articulation 



Pig. 19. — Dendroctonus valens: Mesotergum and mesopleurum. a, Lateral arm of prephragma and 

 preseutum; 6, wing root or connecting membrane; c, lasal margin of elytra; d, radial plate; e, flexor 

 plate; ), median plate; g, scapular plate; h, subscapular plate; i, sutural or anal margin; j, preepistemal 

 process; ft, clavicle condyle; I, eoracoidal condyle; m, scutellum; n, lateral margin of elytra; o, arm of 

 preepistemal process; strise 2-10; interspaces 2-11; p, lateral arm of postphragma; g, pleural claviculus. 

 (Original.) 



the posterior third and dorsal area of the tergum, leaving but a 

 small triangular area exposed between the thorax and inner angles 

 of the elytra. Upon removing the prothorax and elytra this segment 

 is found to represent most of the primary and secondary divisions 

 of the normal segment. 



MESOTERGUM. 



The mesotergum (fig. 19) is rectangular in form, with the pre- 

 seutum occupying two-thirds of the area, while the scutum, scutellum, 

 and postscutellum are less clearly defined or rudimentary. 



Preseutum. — It is evident that the large subtriangular dorsal sec- 

 tion represents the preseutum, as indicated by the evident prescutal 

 lobe and prescutal process, attachment of wing accessories, etc. 



