24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 94 



The epimeron (fig. 3 A, epm. II) appears as a distinct sclerite on 

 the ventral surface of the mesothorax but is united to the episternum 

 on the dorsal aspect to form an undifferentiated pleuron. Posteriorly 

 it overlaps the end of the metathoracic sternum and episternum, and 

 forms the lateral wall of the mesothoracic coxal cavity. Its surface 

 bears a few long sparse setae, similar to the adjacent area of the epi- 

 sternum, and has also the minute punctures. The dorsal aspect of 

 the pleuron bears no setae but is strigulose as described above. 



From the dorsal side of the anterior projections of the mesothorax 

 arise the elytra. Discussion of the articulation of these will be left 

 for the section dealing with the wings. 



The trochantin of the mesothorax (figs. 3 A, th, 4B) is smaller 

 than that of the prothorax but is similar in arrangement and structure. 

 It is an arcuate sclerite, nearly three times as long as wide, and taper- 

 ing distally to form a blunt condyle for the coxa (trla). Its proximal 

 portion forms a condyle that articulates with the projecting corner 

 of the episternum (mtla). Its ventral or ectal surface is thickened into 

 a broad ridge, and the proximal ental part is submembranous. A single 

 long seta is set in a large puncture at the middle of the longitudinal 

 elevation, and the surface is longitudinally strigulose. 



The metathorax is the caudal one of the three thoracic segments 

 and is larger than either of the others. It is very closely united to the 

 mesothorax in front and to the abdomen behind. The tergum is in 

 rather close contact with the tergite of the first abdominal segment, 

 whereas the sternum is rather loosely joined by membrane to the 

 sternite of the third abdominal segment. 



The tergum of the metathorax (figs. 3 A, 4 F) is divided into five 

 parts: The prescutum (psc), the two separated scutal areas (set and 

 sett), the scutellum (scl and sclt), and the postnotum (pn). The 

 prescutum, scutum, and scutellum are fundamental parts of the tergum, 

 but the postnotum or postscutellum is a secondary sclerite formed 

 from the intersegmental membrane caudad of the metatergum and 

 subsequently joined to it (see Snodgrass, 1909). 



The central triangular part of the metatergum is the scutellum. It 

 is separated from the two scutal areas by two internal ridges, the 

 V-ridges (figs. 5 A, 4 F', vr), and two curved sutures. It is sepa- 

 rated anteriorly from the prescutum by a membranous area, and pos- 

 teriorly from the postnotum by a suture (acs) extending between the 

 bases of the wings. Since the posterior margin of the scutellum is mor- 

 phologically continuous with the hind margins of the wings, this area 

 is considered as extending laterad along the suture to the wings, and 

 it is therefore fused with the posterior part of the scutum on each 



