1972] 
Hlavac — Prothorax of Cole opt era 
125 
Almost without exception, the pleuron is divided into an external 
section and an internal, invaginated region, the endopleuron, that is 
concealed by the notum (figs. 2, 7, 9, PI, EndPl). The rim of the 
external portion may be completely folded over, broadly so anteriorly 
and posteriorly to form flanges, parts of paired articulation-collars 
and quite narrowly so ventrally forming half of membranous sternal 
and trochantinal attachments and part of the coxal articulation (figs. 
2, 4, 9 ANFL, APLFL, PNFL, PPLFL, RFM, AF, VF, PF). 
These anterior notal, sternal, and sometimes pleural flanges pro- 
duce a complete articulation-collar or socket which encloses the pos- 
terior aspect of the head, cervical membrane, and, if present, cervical 
sclerites. Likewise, the posterior notal flange, and sometimes a pleural 
Figs. 1-5. Prothoraces of Archostemata and Myxophaga. 
Figs. 1, 2. Lateral external and internal views of Priacma serrata (Ar- 
chostemata, Cupedidae). 
Figs. 3, 4. Same of Pryopteryx britskii (Myxophaga, Torridinicolidae). 
Fig. 5. Lateral view of Hydroscapka natans (Myxophaga, Hydrosca- 
phidae). 
Margins of enclosed structures indicated by dashed lines. 
