34 THE SCOLYTID BEETLES. 



METAPLEURA. 



The metapleurum is well developed and distinctly represented by 

 the two longitudinal sclerites, episternum and epimenim (figs. 3, 

 20), with their anterior dorsal angles greatly produced to form the 

 pleural clavicula with its clavicle and coracoidal processes. 



Pleural suture and apodeme. — The pleural suture marks the line of 

 division between the episternum and epimerum, and extends from the 

 dorsal angle of the coxae to the apex of the pleural clavicula and 

 between the clavicle and coracoidal process. That this is the true 

 pleural suture is indicated by the corresponding prominent pleural 

 apodeme. It is also quite evident that the episternum corresponds 

 to the hypopleurites and the epimerum to the epipleurites of the 

 abdominal segments (figs. 3, 22). 



Episternum. — The episternum is exposed when the elytra are 

 closed (fig. 2). The suture between it and the sternum is distinct 

 and nearly straight, with the anterior end curved toward the coxa. 

 The posterior ventral angle is oblique and joins the posterior dorsal 

 angle of the sternum; from here the posterior margin is oblique to 

 its acute junction with the epimerum and the dorsal angle of the 

 coxal cavity. From here the dorsal margin is acutely elevated to 

 fit into the anterior lateral groove of the elytron, and is nearly parallel 

 with the ventral margin to the preepisternum. 



Preepisternum. — The preepisternum appears to be represented by 

 the narrow declivous anterior section of the episternum connected 

 with the anterior basal area of the pleural clavicula and is apparently 

 involved in the formation of the clavicle process. The clavicle disk 

 evidently represents one or both of the paraptera of certain other 

 insects and belongs to the prepleura. It is situated immediately 

 anterior to the preepisternum. It is large, prominent, and partially 

 exposed, and is connected by a chitinous tendon to the side of the 

 clavicle process. This disk supports the set of large clavicular or 

 sterno-pleural muscles, the opposite ends of which are attached to the 

 sternum and sternellum. 



Epimerum. — The epimerum is situated between the pleural suture 

 and the tergum. With the exception of the extreme posterior ven- 

 tral angle of the postepimerum it is covered by the elytra. The 

 anterior dorsal angle is strongly produced to form the coracoid pro- 

 cess. The ventral area is chitinous and is joined to the episternum 

 by the pleural suture, while the dorsal area is submembranous tc 

 membranous to its junction with the base of the wing membrane. 



Postepimerum. — The posterior ventral angle and posterior lateral 

 section represent the postepimerum, as is indicated by its articula- 

 tory junction with the poststernellum (fig. 20, p). The posterior 



