12 



THE SCOLYTID BEETLES. 



is entirely obscured, as in Pterostictius. It serves the important 

 function of a rigid bridge over the oral foramen and support for the 

 clypeus, labrum, and epipharynx, and at its lateral angles provides 

 the necessary rigid support for the dorsal articulation of the man- 



Mandiblt 



eral impression 



il axillary palpus--^, ^ \ ,, 



.Labial palpu*/ 



Antennal scrobe 



FIG. 4.Dendroctonus valens: Head, dorsal and lateral aspects. A , Dorsal aspect of head; B, lateral aspect 

 of head; C, dorsal aspect of right mandible; D, ventral aspect of right mandible; c, dorsal area; b, dorsal 

 impression; c, anterior condyle; d, median fossa; e, median condyle;/, posterior fossa; g, basal ridge; ft, 

 apical tooth; i, acute margin;,/, subapical tooth; fc, median tooth; I, molar; m, anterior condyle; n, me- 

 dian fossa; o, posterior condyle; p, lateral area; r, dorsal bristles of mandible; s, lateral bristles of man- 

 dible; t, epistomal bristles; u, lateral angle of epistoma. (Original.) 



dibles. In fact the latter function serves to distinguish it from other 

 parts. The median area is variously and sometimes greatly modified 

 in insects of the same order or family, and it appears that in Coleop- 

 tera generally this element is of much greater taxonomic value than 

 has been usually recognized heretofore. 





