THE GENUS DENDROCTONUS. 27 



primary and secondary divisions are not indicated by lines or sutures, 

 but the corresponding areas are suggested by peculiar characters of 

 sculpture and vestiture, which are of more or less taxonomic impor- 

 tance, and thus may be arbitrarily indicated, as in figures 16 and 17, 

 to serve as guides to the location of characters in comparative study 

 and description. 



Pronotum. The pronotum is the dorsal or tergal area of the pro- 

 thorax, as defined by the anterior, posterior, and lateral margins. 

 There is considerable specific variation in its structure, sculpture, and 

 relative proportions. It ranges from about one-fourth to about one- 

 third broader than long, with about the same range of difference in 

 the width of the posterior and anterior areas. In some species the 

 lateral margins are nearly parallel, while in others they are distinctly 

 convergent and constricted anteriorly. The anterior margin is 

 broadly sinuate, while the vertex or dorsal margin of the posterior 

 declivity is bisinuate. The anterior area is broadly transversely 

 impressed, except in the females of some species, where the median 

 section of the area is transversely elevated. The posterior declivity, 

 which perhaps represents the postscutellum, is more distinctly 

 exposed and defined in this genus than it is in allied genera and is 

 therefore an important character of generic distinction. The pleural 

 and sternal areas are indicated in figure 17. 



Episternal area. The episternal area is limited dorsally by the 

 lateral margins of the notum, ventrally by the smooth exocoxal 

 area, posteriorly by the epimeral area, and anteriorly by a preepis- 

 ternal impression or in some species by a ridge. The sculpture of 

 this area is quite variable and in some species furnishes characters of 

 considerable value. 



Epimeral area. The epimeral area is represented by a flattened, 

 smooth space situated between the roughened episternal area and the 

 posterior margin of the prothorax and between the coxae and the 

 basal angle of the notal area. 



Sternal area. The entire sternal area between the anterior and 

 basal margins is largely occupied by the coxal cavities, which are 

 separated by the very narrow intercoxal or sternellar piece. The 

 elevated anterior margin evidently represents the presternum, while 

 the sternum is quite clearly defined by a nearly vertical flat to con- 

 cave space between the presternum and the coxse, the lateral limit 

 being indicated by the smooth, shiny exocoxal area between the coxae 

 and the episternal area. The sternum proper is quite variable, rang- 

 ing from concave, smooth, and shiny, without trace of a median lon- 

 gitudinal line to nearly flat, roughened, or with a median subcari- 

 nate line; but apparently none of these minor characters is suffi- 

 ciently constant, even within the same species, to be of much taxo- 

 nomic value. 



