42 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



antecostal suture (acs). The prescutal ridges and their sutures (ps, 

 ps) are much weaker than those of the mesotergum, but they are not 

 confluent medially with the antecostal ridge and suture, and the lateral 

 prescutal triangles {Psc, Psc) appear to be continuous across the back 

 in a narrow, weakly sclerotized area deflected into the antecostal 

 suture (acs). 



2Ph Pc 



aPh 



R,d AxC 



Fig. 24. — The metathoracic tergum and postnotal plate of Dissosteira. 



acs, antecostal suture; ANP, anterior notal wing process; lAx, first axillary, 

 4AX, fourth axillary ; AxC, axillary cord ; Em, lateral emargination of tergum ; 

 n, prescutal lobe to which base of subcostal wing vein is attached ; 0, tergal lobe 

 to which posterior end of first axillary articulates ; p, tergal arm supporting 

 anal veins of wing (see fig. 47 B) ; Pc, precosta; 2Ph, second phragma: PNs, 

 postnotum; ps, prescutal suture; Psc, prescutum; Rd, posterior fold of tergum 

 (see fig. 25, RdO ; s, s, sutures of secondary tergal ridges; Scl, scutellum; Set, 

 principal part of scutum; set, set, subdivisions of scutum. 



The surface features of the scutal and scutellar regions of the meta- 

 tergum have even less relation to the generalized structure of a wing- 

 bearing tergum than do those of the mesotergum, because the tergal 

 ridges (fig. 23) are here almost completely suppressed, and the exter- 

 nal characters are the result of secondary inflections which produce a 

 topographical pattern quite independent of the primary divisions of 

 the tergum (fig. 5). Most of the scutal region (fig. 24, Set) and the 



