56 THE SCOLYTID BEETLES. 



of the spines. The median process of the scutelhim is prominent and 

 the posterior or scutellar ridge is distinct. The base of the elytra is 

 obhque and elevated, and its integument continuous with that of the 

 tergum and scutellar ridge. The sternum is situated between the 

 mesocoxse and the trochantins of the prothoracic leg. 



MetatJiorax. — The metatergum is prominent and has the usual dor- 

 sal or scutellar groove. The transverse posterior or scutellar ridge is 

 distinct and joined at its ends with the basal angle of the wing pads. 

 Each of the scutal lobes bears a pair of spines. It differs from the 

 metatergum of the adult mainly in the absence of the prescutum and 

 postscutellum, as defined by external elements. 



Abdominal tergites (fig. 38). — There are nine tergites visible dor- 

 sally and a very small tenth visible ventrally. Tergites 3 to 6 are 

 armed more or less distinctly with dorsal, lateral, and pleural spines. 

 The dorsal spines are located each side of a narrow dorsal groove; 

 the pleural spines on the epipleura posterior to the spiracles, and the 

 lateral spines are situated between the dorsal and pleural. The size 

 of the pleural spines and the size and number of the dorsal and lateral 

 ones are quite variable and of considerable importance in defining 

 the minor divisions. Tergites 7 and 8 are usually unarmed, but, as 

 in the adults, show sexual differences in their relative prominence; 

 9 has the median lobe short, but the pleurites are greatly enlarged 

 and each is armed with a prominent caudal spine. 



The four transverse divisions of the segments are quite clearly indi- 

 cated in tergites 1 to 6. Tergites 7 and 8 show two divisions, the first 

 representing prescutal and the second the scutal and scutellar com- 

 bined, while tergites 9 and 10 are undivided. It is interesting to 

 note that the dorsal and pleural armatures are borne by what is evi- 

 dently the scutellar division, and that the spiracles are in the prescutal 

 division, thus indicating that the prescutal represents the first pri- 

 mary division and the combined scutal, scutellar, and postscutellar 

 represent the second primary division. 



Abdominal sternites. — There are eight exposed abdominal sternites. 

 These are sternites 3 to 10, 1 and 2 being concealed beneath the 

 metacoxse, as shown in figure 38. 



Abdominal 'pleurites. — Epipleurites and hypopleurites 1 to 8 are 

 clearly defined in the removed abdomen (fig. 38), but in 9 and 10 only 

 the epipleurites are represented, as indicated by the pleural suture. 

 The pleural suture is distinct to the ninth segment, where it joins the 

 lines marking the dorsal and ventral limits of the pleural division. 



Spiracles. — There are nine spiracles in each side of the body, one 

 large mesothoracic spiracle situated between the posterior lateral 

 margin of the prothorax and the anterior ventral angle of the elytral 

 pad, and eight abdominal ones, each in its respective epipleurite. 



