THE GENUS DENDROCTONUS. 



37 



The median area is triangular in form and covered with bristles 

 and hairs rising from variously formed bases. On its face and some- 

 times on the posterior area there are a few irregularly arranged 

 truncate tubercles (J), m), each bearing a short, stiff bristle. These 

 may possibly function as sense organs. 



The membranous lobes are subovate, finely sulcate, and thickly 

 clothed with rechning microscopic spines (o). The exact function 

 of these lobes is not known to the writer. Tergites 4, 5, and 6 have 

 similar lobes. The other dorsal and ventral characters are made 

 sufficiently clear in D and E. 



Fig. 24. — Bendroctonus valens: Female, abdominal tergites 7 and 8. a, Anterior arm of epipleurite 7; 

 6, membranous area surrounding spiracle; c, membranous lobe; d, epipleural process; e, hypopleural 

 process of stemite 8; /, pleural opening; g, anal space; h, ventral fold; i, rudimentary spiracle; j, epipleural 

 disk; fc, median membranous connection of the lateral sections of stemite 8. (Original.) 



Tergite 8 {A, B) is the pygidium. This, in the male, is always 

 larger and more exposed beyond the margin of tergite 7 than in the 

 female. The relative proportions, as compared with 7, and the dorsal 

 and ventral characters are clearly shown in A and B. The lateral 

 arms serve as attachments for pleural muscles and articulating mem- 

 brane and ligaments. In C the abdominal sternite is added to show 

 its relative position and proportions. 



Pygal tergites of the female. — -The P3^gal tergites of the female are 

 shown in figure 24, A, B, C, D, E, F. 



Tergite 7 (propygidium) is much more simple in structural details 

 in the female than in the male, and tergite 8 (pygidium) is also more 

 simple and shorter, being almost or entirely covered b}^ 7 when in 

 normal position. 



The characters of sternite 8 are shown in D, the most important 

 of which is the median membranous area. 



