22 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, 82 



In Gnathotriclius, the pregula (figs. 6, 7, I'r) is always without 

 sculpture or hairs. The very distinct specific modifications are de- 

 scribed in the following key : 



A — Pregula flat, triangular, not produced anteriorly, its anterior mar- 

 gin continuous with those of the gena. 



Gn. sulcatus Lee. 

 AA — Pregula convex, produced anteriorly, its anterior not continuous 

 with those of the gena. 



B — Pregula very convex, extending far beyond the genal 

 margin. 



Gn. retusus Lee. 

 BB — Pregula feebly convex, extending slightly beyond the 

 genal margin. 



Gil. inateriarius Fitch. 



Epicranium. — The remaining lobes of the cranium situated between 

 the epicranial suture, the gula, and the foramen bear the compound 

 eyes (figs. 4-6, Ey), the antennae and the articulations of the mouth- 

 parts. For merely descriptive purposes these lateral areas of the 

 cranivmi have been divided into several regions. The occipital area 

 (figs. 4, 6, Oc) surrounding the occipital foramen is not limited an- 

 teriorly in Gimthotrichus. However, there occur obscure lines which 

 may be regarded as homologous with the occipital suture. The epi- 

 cranium or parietals (Crampton), the gena, and the vertex do not 

 show any sculpture which exhibits specific differences. The hypo- 

 stoma (Hopkins) (figs. 6, 7, Hy), an area corresponding to the epi- 

 stoma, which like the former belongs morphologically to the epicra- 

 nium, is well developed.^ It is in the form of a semicircular band and 

 bears at its extremities the ventral articulations (figs. 6, 7 b) of the 

 mandibles. From the oral aspect it is visible ; from the ventral, it is 

 hidden by the pregula and the gena. 



Other regions, such as the pregena (Hopkins), etc., are not at all 

 distinct or limited and are therefore of no interest in this discussion. 



THE APPENDAGES OF THE HEAD 



THE ANTENNAE 



The antennae present good generic characters ; the species modifica- 

 tions are less important. The sexual differences are distinct also. All 

 the longer setae of the antennae are feathered. 



* The hypostoma, as the term is used here, or the ventral angles of the postgena, 

 is the bearer of the maxillare and not the labium. A submentum, as this term 

 was used by Hopkins in Dendroctonus, is not defined by sutures. 



