22 



THE SCOLYTID BEETLES. 

 THE THORAX. 



The thorax, as usual, consists of three distinct segments. The 

 prothorax freely articulates with the mesothorax, but the pleurites 

 and sternites of the mesothorax and metathorax are rigidly con- 

 nected. The combined length of the ventral areas of the three 

 thoracic segments is slightly greater than that of the ventral area of 

 the abdominal segments, while the combined length of the dorsal 



FIG. 14. Dendroctonus valens: Mandible, a, Apical tooth; b, subapical tooth; c, median tooth; d, 

 molar tooth; e, dorsal area; /, dorsal bristles or setae; g, dorsal impression; h, transverse ridgs; i, pha- 

 ryngeal process; j, retractor tendon; fc, lateral area; I, lateral bristle; m, lateral impression; n, anterior 

 condyle; o, basal ridge; p, median fossa; q, median condyle; r, posterior fossa; s, condyle of ventral 

 articulation; t, basal foramen; u, retractor disk; v, extensor disk; w, extensor tendon. (Original.) 



areas of the thoracic segments is about equal to that of the area of 

 the abdominal segments, or slightly longer. The pronotum is as 

 long as both the mesotergum and the metatergum together. The 

 prosterna and mesosterna are about equal in length, and both 

 together about equal to the metasterna, while the combined length 

 of the thoracic pleura is slightly greater than that of the abdominal 

 pleura. The anterior dorsal margin of the pronotum and the pos- 

 terior margin of the metatergum are greatly extended anteriorly 



