1972] 
Illavac — Prothorax of Coleoptera 
129 
membrane. Peri-coxal and trochantinal membrance enclosed by cowl- 
ings on pleuron, sternum and trochantin (fig. 24). 
Evidence for the primitiveness of individual characters is obtained 
from both extant and fossil forms. 
The tripartite body wall and anterior collar is a major feature 
of the archtypical coleopterous prothorax. This arrangement is geo- 
metrically the simplest way of producing a sclerotized cylinder bear- 
ing paired sockets, i.e., through anterior development and folding of 
dorsal, lateral and ventral elements without shift in relative position. 
Pleural size and structure of three suborders (Archostemata, Ade- 
phaga, Myxophaga) is similar to that of the stem configuration but 
differ from it in having a reduced or internalized anterior flange. 
A relatively small, external, anterior pleural flange is present only 
in some extant members of the Archostemata and Myxophaga. In 
other members of both groups, the flange is even further reduced and 
enclosed by overlap of notal and sternal elements (figs. 1-5, 11, 12). 
In one group of Archostemata (Cupdidae, Ommadinae) and in all 
Adephaga, the anterior flange is absent, and a small anterior pleural 
fold is internalized, frequently by membranous connection of a lobe- 
like expansion of the sternal flange with the notal flange (figs. 8, 9, 
13, 14). In some Adephaga and Myxophaga notal and sternal flange 
rims may overlap but are not connected (figs. 3, 8). The Myxo- 
phaga and Adephaga then overlap the Archostemata at opposite ends, 
of this morphocline. 
In many Mesozoic Coleoptera of dubious subordinal position, the 
notum and sternum are widely separated by the pleuron (e.g., Pono- 
marenko 1969; figs. 74, 102). No internal evidence is available. 
However, since the posterior rim of the head is clearly enclosed by 
Figs. 10-19. Morphology of anterior section of the pleuron and surround- 
ing structures; sclerites slightly disarticulated. 
Figs. 10-15. Internal views. 
Fig. 10. Hypothetical stem configuration. Fig. 10A. Section through plcuro- 
sternal joint. 
Fig. 11. Priacma serrata (Archostemata, Cupedidae, Cupedinae). 
Fig. 12. Cupes concolor (Cupedidae, Cupedinae). 
Fig. 13. Amphizoa insolens (Adephaga, Amphizoidae) . 
Fig. 14. T etraphalerus wagneri (Cupedidae, Ommadinae). 
Fig. 15. Generalized Polyphagon. 
Figs. 16-18. External views of Polyphaga. 
Fig. 16. Peltastica turberculata (Derodontidae) . 
Fig. 17. Sarabandus robustus (Helodidae). 
Fig. 18. Megarthrus robustus (Staphylinidae) . 
Fig. 19. External view of Priacma; sections included above, heavily 
stippled. 
