NO. lO MORPHOLOGY OF GNATHOTRICHUS — SCHEDL 77 



THE THORAX 



The thoracic segments are somewhat larger in size than those of the 

 abdomen. They do not differ from each other in shape but are dis- 

 tinguished by the structure and the development of the setae. The 

 thoracic segments are legless as in the whole super family but the foot 

 calli are distinct. 



Dorsally, the prothorax is distinguished from the other two thoracic 

 segments by the lack of the suture which divides the prescutum 

 (fig. 36) from the fused scutal-scutellar area. However, the prescu- 

 tum is indicated by the corresponding setae. On the meso- and meta- 

 thorax, the prescutum is present as a narrow transverse sclerite (f), 

 near the anterior margin of which the prescutal setae (fi-4) are 

 situated. The scutum (e) and the scutellum are in all three segments 

 fused. The pleural area is fairly well defined by a longitudinal fold 

 ventrally. Latero-dorsally it is fused with the scutal-scutellar area. 

 Another longitudinal fold divides the pleural area into two distinct 

 parts. The part next to the scutal-scutellar area represents evidently 

 the epipleurite (d), the ventral part the hypopleurite (c). The former 

 has a smooth surface bearing setae only ; the latter has the surface 

 covered with minute spines beside the setae. On the sternum two 

 subdivisions are plainly visible, the sternal (a) and the sternellar 

 area (b). The sternellar area or sternellum consists of two large 

 lateral lobes which are connected by a very narrow band medially. 

 The lateral lobes which bear the foot calli are covered with minute 

 spines similar to those in the hypopleurites. There is not enough evi- 

 dence to speak about a poststernellar area in Gnathotrkhus as it 

 should be present in Dendroctonus according to Hopkins. The setal 

 arrangement will be discussed with that of the abdomen. 



THE ABDOMEN 



The abdomen (fig. 36) consists of ten segments, the tenth of which 

 is strongly reduced and present as the anal lobes. The segments de- 

 crease in size slightly towards the apex. Segments one to seven in- 

 clusively are alike in structure and setal arrangement. They differ 

 in structure from the meso- and metathorax in having longitudinal 

 folds which separate the epipleural area from the sternum and the 

 scutal-scutellar area. Also the sternal-sternellar suture is restricted 

 to a membranous fold. The two lateral lobes of the sternellum are 

 apparently not connected medially. The eighth segment does not show 

 signs of the prescutal -scutal suture. Still more reduced is the ninth 

 segment ; it has no sutures or folds but the different sclerites can be 



