THE GENUS DENDROCTONUS. 



19 



Labium proper (figs. 2, 5, A). — In Dendroctonus and other rhyn- 

 chophorous beetles, the mentum, palpifer, glossse, and paraglossa, 

 while more or less clearly indicated, are not represented as separate 

 elements of the labium. Mentum: The mentum articulates with 

 the bifid submentum and completely surrounds the basal portion of 

 the labrum, being subcyhndrical, with the anterior ventral area 

 strongly retuse. Palpifer: The palpifer is represented by the area 

 between the ventral impression of the mentum and the row of 

 palpiferal bristles which define the anterior limit of the mentum. 

 Palpi: The labial palpi are distinct, 3-jointed, and as long as the 

 mentum, or longer, with the first joint longer than the other two, or 

 rarely equal. Ligula: The ligula 

 is situated between the palpi, is 

 thickly set with long lacinial teeth, 

 and occupies the greater part of 

 the dorsal area. It is evident 

 that this ligular area represents 

 the glossas and paraglossa of other 

 insects, and that it is homolo- 

 gous with the galea and lacinia 

 of the first maxilla. 



Maxillx (figs. 2, 5, B, C).— The 

 maxillae (fig. 5, B) have the char- 

 acteristic form of those of all other 

 rhynchophorous beetles and are 

 strikingly different from those of 

 other Coleoptera. The form and 

 relative proportions are shown in 

 the figures. Cardo: The cardo is 

 the stout basal section which 

 articulates with a condyle on 

 the maxillary process of the hy- 

 postomal apodeme. Stipes: The 

 stipes articulates with the cardo and, while it does not appear as a 

 separate piece, it is represented by the posterior ventro-lateral and 

 externo-lateral part of the median section of the maxilla. Palpifer, 

 galea, subgalea, and lacinia: The palpifer is fused with the stipes 

 and is represented by the anterior part of the median section (fig. 5). 

 The palpifer and stipes are also fused with the subgalea on the 

 exto-lateral area, but on the interno-lateral area the line separating 

 the palpifer from the subgalea is distinct, as is also the suture be- 

 tween the latter and the lacinia and galea, which are fused, the latter 

 being represented by a narrow chitinous margin next to the palpus 

 and palpifer. The lacinia is armed on the inner edge with stout 

 lacinial teeth. The length of the base of the subgalea from the apex 

 79980—09 3 



FiG.lO.— J>emdrocto7iMS.-Epistomata. a to I, D. val- 

 ens; m to o, D. simplex; p to s, D. pseudotsugse. 

 (Original.) 



