126 
Psyche 
[September 
flange as well, form an incomplete collar enclosing part of the meso- 
thoracic rim and some intersegmental membrane ( fig. 8 ) . 
The fold forming the anterior sternal flange may continue dorsally 
to join with a pleural or notal rim fold and then extend ventrally 
to form a membrane enclosing joint with the trochantin. Below the 
trochantin, the sternum generally bears a shelf-like, poorly pigmented, 
concave region, the cryptosternum, which supports and is concealed by 
the coxa (figs. 7, 9 CrS). The cryptosternum also bears a pair of 
invaginations or apophyses close to the posterior margin. Frequently, 
the sternum is evaginated medially, forming a projection which may 
extend between, behind, and sometimes above the coxa. Sometimes 
a second, smaller sternallar projection is present as well (fig. 7 Spj, 
SLpj). A complete posterior collar is commonly formed from union 
of either of these projections with notal or pleural projections (figs. 
33. 43, 46, 48, 62, 64). 
Subordinal Differences and the Hypothetical 
Stem Configuration 
There are major differences in pleural size, structure, motility and 
in its trochantinal attachment among the four suborders of Coleop- 
tera. Subordinal configurations can be diagnosed as follows. 
archostemata. Pleuron large, rigid, forming lateral wall of 
segment. Trochantin motile, external. Anterior pleural flange exter- 
nal, small and enclosed, or absent with internal anterior fold. Ster- 
nal joint membranous to solidly fused (figs. 1, 2, 11, 12, 14). 
myxophaga. Pleuron variable in size (figs. 3-5), rigid, fused to 
trochantin. Anterior pleural flange external or enclosed (figs. 3-5). 
Sternal joint membranous. 
adephaga. Pleuron, a prominent part of body wall, rigid. Tro- 
chantin, small, motile, enclosed along with coxal articular region by 
pleural and sternal cowlings. Anterior pleural flange absent, ante- 
rior fold internalized by union of notal and sternal flanges (figs. 8, 
9, 13, 61-65). Sternal joint fused. 
polyphaga. Pleuron greatly reduced in size and fused to tro- 
chantin; this highly variable compound structure may be motile and 
contribute to coxal movement, and may be completely enclosed. No- 
tum and sternum attached anterior to pleuron to form body wall. 
Anterior pleural fold and zone of fusion between pleuron and tro- 
chantin present in a few primitive groups. Sternal joint membranous 
to solidly fused (figs. 6,7, 15-17,23-55). 
