536 



PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxvi. 



(postscutelliim) of Hydrophilus he evidently calls the acroteraite of 

 the first abdominal segment and equates it with the anterior subdivi- 

 sion of the first abdominal tergum of Acridhnn. He appears to dis- 

 regard entirely the intimate connections 

 ^r V pnr of the pseudonotum with the epimeral 



plates belonging to the segment of the 

 preceding notum and its attachment to 

 the preceding notum itself. 



V/P ^ 



TnC 



Fig. 3. — Diagka.m.matic lateral 

 view of any complete wing- 

 beakixg segment, bxternal ; 

 ayp, anterior notal wing 

 PROCESS ; anr, line of an- 

 terior VENTRAL NOTAL RIDGE ; 

 AxC, AXILLARY COPiD ; Cx, COXA ; 

 CxP, COXAL PROCESS OF PLEU- 



EUM ; Epm, EPIMERUM ; Eps, 



EPISTERNUM ; 2V, NOTUM ; IP, 

 2P, El'lSTERXAL PARAPTERA OR 

 PREPARAPTERA ; SP, EPIMERAL 

 PAEAPTERUM OR POSTPARAP- 



TERUM ; Peps, PREEPI STERNUM ; 

 PX, PSEUDONOTUM OR POST- 

 NOTUM ; PNP, POSTERIOR NOTiL 



WING PROCESS ; pnr, line of 



POSTERIOR VENTRAL NOTAL 



RIDGE ; Ppll, POSTPHRAGJIA ; Pt?. 

 PLEURAL SUTURE ; Ps, PRESTER- 

 NUM ; »S', STERNUM ; Tn, tro- 



CHANTIN ; TnC, TROCHANTINAL 

 COXAL CONDYLE ; V, LINE OF 

 VENTRAL V-SHAPED NOTAL 



RIDGE ; WP, PLEURAL WING 

 PROCESS. 



the pleural coxal process 

 heavy pleural ridge or 

 apodeme lying along the 1 



2. The Pleurum and Coxa. 



The key to the structure of the pleu- 

 rum is the pleural suture. To deter- 

 mine this proceed as folloAvs: Find the 

 pleural process that supports the base of 

 the wing; locate the pleural condyle to 

 which the coxa is articulated ; observe the 

 impressed line that extends betAveen these 

 two articular knobs. This is the pleural 

 suture. The episternum lies in front of 

 it, the epimcrum behind it. In wingless 

 forms the pleural suture must be deter- 

 mined by the coxal articulation alone. 

 The suture ma}' be horizontal, in which 

 case the contiguous plates necessarily 

 lie above and below it. Very rarely it 

 is lacking, though such is conspicuously 

 the case in the metathorax of most of 

 the Hymenoptera. Internally the pleu- 

 ral suture forms a large ridge along its 

 entire length, and this pleural ridge is 

 of great assistance in determining the 

 pleural suture when the latter is obscure 

 or when there are other similar sutures 

 externally. 



The plan of any wing-bearing thoracic 

 pleurum is illustrated diagrammatically 

 by figs. 3 and 4. Externally (fig. 3) 

 is seen the pleural suture (PS) extend- 

 ing upward to an arm bearing the wing, 

 the pleural wing process (AVP) and ven- 

 trally to a condyle bearing the coxa. 

 (CxP). InternalW (fig. -i) is seen the 

 entopleurum [PR), a large ridge-like 

 ine of the pleural suture, terminating in 



