71 



tending caudo-cephalad along the middle of the back, with 

 strongly chitinized margins which project slightly mesad 

 over the depression. On the inner surface of the elytra, 

 near the base of the mesal margins, there are two, slight, 

 projecting processes. These small processes have strong, 

 acute margins, which project slightly laterad. When the 

 elytra are closed, the raised processes fit into the groove of 

 the metanotum, and the laterad-projecting margins of the 

 processes lie under the mesad-projecting margins of the 

 groove, the whole structure forming a means for the firm 

 holding of the elytra over the dorsum of the body. The 

 firm holding of the elytra is further aided by the inflexed 

 lateral margins and by the close dovetailing of the mesal 

 margins along the middle of the back. 



Ventral aspect. — As in the other thoracic segments this 

 includes both the sternum and the pleural sclerites. 



Metasternum. — The metasternum is, as the mesosternum, 

 best described as saddle-shaped. It has a rather broad, 

 blunt tongue, projecting cephalad between the mesocox?e to 

 meet the caudad-projecting tongue of the mesosternum. It 

 presents, also, an acute-angle process, projecting caudad 

 between the cephalic halves of the metacoxae. The " sad- 

 dle-fiaps," or lateral lobes of the metasternum expand later- 

 ad, and their cephalic margins, concavely rounded, form the 

 caudal boundaries of the mesocoxal cavities. There is a 

 line or suture running transversely across the metasternum 

 near the caudal margin which does not reach the lateral 

 margins. That portion of the metasternum caudad of this 

 suture is called the atitecoxal piece of the metasternum. 

 ' Episternum. — The rhomboidal episternum .is the largest of 

 the pleural sclerites. 



Epimeron. — The trapezoidal e/>i/iie>on, though smaller than 

 the episternum, is broader, and more conspicuous than that 

 of either of the other thoracic segments. 



