36 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



Sternellar area. — The sternellar area is strongly produced poste- 

 riorly and internally defined by a suture from the postero-sternellar 

 piece. 



Poststernellar area. — This piece (Pstr) is a narrow continuation 

 from the sternellar area. Externally both are covered with long 

 bristles. 



THE METATHORAX 



Metatergum. — The general appearance and structure is illustrated 

 in figures i, 2 and 3, which also show the two main parts, namely 

 the notum and the postnotum, or pseudonotum, as the postnotum is 

 often called. The latter is well developed and connected with the 

 notum by a transparent membrane (a). The dorsal aspect of the 

 metatergum is shown in figure 17; the inner in figure 19. 



Metanotum. — The metanotum (figs. 17, 19) is typical in Gnatho- 

 trichus in so far as the prescutum (Psc) is only loosely connected 

 with the scutvmi (Set). The connection consists medially of a trans- 

 parent membrane (b) ; laterally the extreme ends of the posterior 

 prealar process (d) are fused with the lateral margin of the scutular 

 lobes. In this connection it should be mentioned that Hopkins' pre- 

 scutal lobe seems more likely to be a part of the scutum than of the 

 prescutum. Other modifications are the overlapping of the scutum 

 beyond the posterior prealar process and the development of the 

 scutellum. 



The metanotum is clearly defined into three transverse divisions 

 which are the prescutum, the scutum and the scutellum. 



Prescutmn. — The prescutum (Psc) forms a well developed trans- 

 verse band extending from pleuron to pleuron. Medially it is bent 

 downwards, forming a ventral reflected lobe which may correspond 

 to the prephragma in other insects. A precosta is not present as a 

 plate defined by lines or sculpture. On the level of the interior origin 

 of the anterior apodeme a suture extends interiorly separating the 

 posterior prealar process from the prescutum proper. This process 

 extends laterally, is covered by the scutular lobe and is fused with 

 it at the extreme end. From the antero-lateral corners of the prescu- 

 tum proper originate two prominent hooks, the anterior prealar proc- 

 esses (f). Laterally to the anterior prealar process are two disklike 

 formations on each side (g, h) connected with the posterior prealar 

 process. According to Hopkins, the posterior disk (prescutal disk) 

 serves for the small muscles connecting it with the pleural clavicula. 

 A rather intensive investigation would be necessary to determine the 

 purpose of all these formations and homologize them with similar 

 equivalent parts in other groups. 



