130 
Psyche 
[September 
the prothorax in these forms, it is reasonable to infer the existence of 
a tripartite anterior collar. In other fossil beetles, the notum and 
sternum extend in front of the pleuron. This could represent either 
a stage of anterior pleural reduction as in figs, 3, 4, 12, or a distinct 
noto-sternal joint. The evidence is ambiguous. 
Based on the geometry of major sclerites, and structural variation 
in extant and fossil forms, a three element body wall and anterior 
collar is taken to be primitive for Coleoptera. The distribution of 
extant forms evolved though variable, possibly, parallel reduction of 
the anterior flange. 
A separate, motile trochantin occurs in the Archostemata, Ade- 
phaga and in other holometabolous orders. The trochantin and pleu- 
ron are fused in the Myxophaga and Polyphaga. A separate tro- 
chantin is doubtless a primitive trait in Coleoptera. 
The almost universal presence of membrane enclosing rim-fold 
joints between major sclerites, and moving parts within both extant 
and fossil forms is evidence for the primitiveness of these articula- 
tions within the Coleoptera. A rigid rim-fold joint is produced by 
medially bending the edges of two sclerites to form a pair of flat- 
tened, normally horizontal articulation surfaces which may bear 
tongue-groove devices (fig. 10A). Attachment membrane extends 
between the margins of the two sclerites and is enclosed. In all ex- 
tant forms, the body wall elements are connected with mebranous 
rim-fold joints (frequently in primitive members of higher taxa) or 
are solidly fused together, sometimes with a distinct internal carina 
and often without the slightest vestige of a suture (figs. 9, 59, 50). 
Rigid rim-fold joints seem to be universally present in fossil Coleop- 
tera, as well. 
Except in extreme surface grade polyphagans, membrane around 
the coxa and trochantin is enclosed by loose rim-fold joints or both 
structures may be entirely enclosed by cowlings, see below. There 
is no obvious membranous band between moving parts in the fossil 
Coleoptera depicted by Ponomarenko (1969). It is assumed, then, 
that rigid and loose rim- fold joints are primitive characters in the 
Coleoptera. 
Except for the Polyphaga, Recent suborders and early fossil Cole- 
optera are similar to the stem configuration in basic organization. 
The major differences between the Adephaga, Archostemata, and 
Myxophaga are either simple modifications of structural details (re- 
duction of anterior pleural flange, trochantinal fusion) or adaptations 
for improving structural integrity (enclosure of coxal articular re- 
gion and trochantin in the Adephaga). The great differences between 
