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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



not set off by sutures as in the mesosternum. The small triangular 

 plates {t, t) bordering the coxal cavities appear to be subdivisions of 

 the sternellar lobes rather than subcoxal laterosternal pieces, since the 

 ventral arms of the pleurites in the nymph (fig. 27 A, Ls) form only 

 the membranous folds beneath the coxal cavities in the metathorax. 



There is no spina associated with the metasternum. Crampton 

 (1918) says the spinal pit has disappeared from the metasternum, but 

 he gives no evidence of its former existence. As we have seen, the 

 intersternal sclerotization between the metasternum and the first ab- 

 dominal sternum remains as an integral pai't of the latter, or disappears 



o^ 2Spn 



Fig. 31. — Inner surface of ventral pleuro-sternal region of mesothorax. 



Bs, basisternum; CxCi, coxal cavity; Epm, epimeron; Eps, episternum; 

 Isg, intersegmental groove ; ./', ridge of prepectal suture ; k, furcal ridge ; PIA, 

 pleural arm ; PIR, pleural ridge ; PIS, pleural suture ; Ppct, prepectus ; S3, an- 

 terior part of metasternum ; SA, sternal apophysis ; SI, sternellum ; 2Spn, second 

 spina, united with furcal ridge of mesosternum. 



when the first abdominal sternum becomes rudimentary. In Dissosteira 

 the ventral muscles of the first abdominal segment (fig. 35, IS) are 

 attached anteriorly on a weakly developed ridge (Ac) which crosses 

 the first abdominal sternum between the angles of the sternellar lobes 

 of the metasternum. The line of this ridge appears externally as a 

 faint transverse suture (fig. 30 A, D, acs). The ridge (fig. 35, Ac), 

 therefore, is the antecosta of the first abdominal sternum, and the 

 representative of the spinae of the prothoracic and metathoracic sterna. 

 The median plate dovetailed into the metasternum (figs. 30 A, D, 35, 

 Pc) is the enlarged precosta of the first abdominal sternum. It cor- 

 responds exactly with the postnotal plate of the metathorax (fig. 25, 

 PNz), which is an extension of the precosta of the first abdominal 

 tersum. 



