18 THE SCOLYTID BEETLES. 



smoother surface and by the presence of the compound eye, which is 

 situated on the side of the head near the base of the antennae. The 

 anterior end of the epicranial suture defines the anterior dorsal limit 

 of the epicranium, designated as the vertex, while the gena is repre- 

 sented by the ventral area between the eyes and the gular suture. 

 The epicranial suture is more distinct in some species than in others. 



Eijes. — The eyes vary from slightly oblong oval to oblong ovate 

 and are obliquely placed in the anterior angle of the epicranial area, 

 just posterior to the base of the antennse. The variation in form 

 within the genus and within the same species is shown in figures 1 to 

 6 and 15. There are about four hundred facets, which are small and 

 densely placed. 



Occiput (figs. 4, 5). — The occiput is not clearly defined, as it is in 

 Pterostichus , but the posterior area of the cranium to the occipital 

 foramen may be designated as the occipital region or area. 



Occipital foramen (fig. 5). — The posterior opening in the head, or 

 occipital foramen, is small as compared with the oral foramen. The 

 invaginated wall forms a part and posterior support to the tentorium, 

 and the dorsal apodeme is continuous with the epicranial suture. 



Gula. — The gula is not represented by a space defined by two 

 longitudinal sutures, as in most Coleoptera other than the Rhyn- 

 chophora. The gular apodemes are present (fig. 5, D), but the gular 

 space is invagmated, so that there is but a single gular suture. 



Pregula. — In Dendroctonus there is a small sclerite immediately 

 anterior to the gular suture (figs. 5, 6) which is distinctly separated 

 from the gula and gense by an invaginated apodeme, laterally from 

 the pregena by an evident external line, and anteriorly from the 

 hypostoma by a ridge which defines the anterior margin. In the 

 rostrate beetles this is extended with the pregena and forms a more 

 or less distinct gular space of the rostrum to a similar anterior space 

 which supports the so-called gular peduncle, or submentum. There- 

 fore it appears that the term pregula should serve to distinguish this 

 important element, which is also more or less distinctly represented 

 in Coleoptera other than the Rhynchophora. (Compare figs. 6, 7, 8.) 



Gena. — The gena is not defined by lines, but it is represented by 

 the ventral area between the gular suture and the epicranial area, 

 ;as described under epicranium and gular suture. 



Pregena (figs. 5, 6). — The pregena is a distinct pleural area situ- 

 ated between the base of the antennse and the pregul^, bounded 

 posteriorly by the genal area and anterior angle of the epicranium, 

 and anteriorly by the hypostoma. 



Submentum (figs. 5, 6). — The submentum is represented by a 

 bifid process or me<lian extension of the hypostoma, and is sup- 

 ported by two stout, braces rising from the large transverse rostral 

 apodeme beneath, the posterior angle of the pregula. 



