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Psyche 
[September 
or more of the following limitations: small and/or poorly chosen 
sample ; superficial analysis of raw data, or none at all ; impoverished 
treatment of adaptive phenomena. There are few even moderately 
comprehensive studies of structural variation; see Arnett (1967) for 
list and brief descriptions. And, many glaring problems have not been 
dealt with. For example, prothoracic characters have long been used 
in subordinal diagnoses, yet detailed comparisons of representatives of 
each taxon have not been made. 
Since ecological differentiation and thoracic adaptation are so in- 
timately related, understanding the locomotory system is particularly 
important for the future development of beetle systematics. Due to 
size and diversity of the group, work on this functional complex is 
neither easy nor quickly accomplished. The only feasible compromise 
is to select a natural subunit of this system for detailed study. The 
prothorax is the obvious, initial choice. 
Prothoracic structure and mechanics are simple as compared to 
those of the two pterothoracic segments where both ambulatory and 
flight functions are combined. Differences in size, structure and func- 
tion in the prothorax are readily perceived and correlated with phys- 
ical demands of various environments. Furthermore, details of pro- 
thoracic mechanisms are commonly diagnostic of higher categories. 
The interplay between adaptive phenomena and historical develop- 
ment in the prothorax is considered below at 2 levels: origin of the 
coleopterous prothorax and variation within the two biologically 
diverse suborders. 
The generalizations and evolutionary hypotheses presented here 
are based on dissection of over 600 selected genera, and external ex- 
amination of many others. Raw data, primarily drawings, group 
diagnoses, and discussions of variation within major taxa, will be 
presented elsewhere as will results of a current study of pterothoracic 
structure. 
Basic Structure 
The walls of the rigid, cylinder-like prothorax of Coleoptera are 
always formed by the notum dorsally, by the sternum ventrally, and, 
in some forms, the pleuron forms distinct lateral walls (figs. 1-9). 
The trochantin, a small, sometimes movable sclerite, is attached to 
the sternum and pleuron and along with the latter articulates with 
the coxa, the basal leg segment (figs. 2, 7 Tn). The coxa also 
rests on and sometimes mechanically articulates with the posterior 
section of the sternum — the cryptosternum (fig. 7 CrS). 
