NO. 13 



STAJ'llVLINIDAE BLACKWELDER 



63 



The mentuni is frequently united to the submentum between the 

 projecting anterior corners of the latter. It is usually trapezoidal 

 in form but may be variously lobed in front, as in Leptochirus (fig. 

 18 G), Oxyponis (fig. 18 A), and Liparocephahis (fig. 18 E). It fre- 

 quently bears a few large setae and is nearly always sparsely set with 

 large pores. 



Fig. 18. — Intrafamily variation in the form and structure of the 

 labium. (Only the basal segment of the palpi shown.) 



A, Oxyponis lateralis Grav. B, Osorius imiiuiiis Shp. C, Lathriiiiaciiiii pictiiiii 

 Fvl. D, Baryodina himaciilata Grav. E. Liparoccplialiis brcz'ipciniis Makl. F, 

 Trigoiuinis crotchi Lee. G, Leptochirus mcxicauus Er. H, Gastrolohiiiin bi- 

 color (Grav.). 



The prementum is frequently only partly sclerotized. In Trlgonurus 

 (fig. 18 F) there are three small triangular sclerites lying in the mem- 

 brane between the paraglossal lobes; in Osorius (fig. 18 B) there is 

 a single large quadrate plate anterior to the base of the palpi ; in 

 Oxyponis (fig. 18 A) the entire basal part of the prementum is sclero- 

 tized as a long plate ; and in other forms there is more or less sclero- 

 tization of the area between the mentiim and the base of the palpi. The 

 5 



