THE RELATIONSHIP OF THE PROTOPERLARIA AND 
THE ENDOPTERYGOTA 
By Phillip A. Adams 
Department of Biological Sciences 
University of California, Santa Barbara 
The first worker to recognize that the Protoperlaria were 
a group distinct from the Protorthoptera, and probably 
ancestral to the Plecoptera, was Tillyard (1928a, b). The 
relationship of these orders has been discussed in more 
detail by Carpenter (1935). That the Protoperlaria might 
be of far greater phylogenetic significance has not gen- 
erally been appreciated. Although the suggestion that the 
Protoperlaria were close to the ancestral form of the En- 
dopterygota was made by Bradley (1939, 1942), this re- 
lationship has not previously been documented. 
While a comparison was being made between the wings 
of the protoperlarian, Lemmatophora, and the neuropteran, 
Sialis, in an effort to determine the venational homologies 
of the latter, it became apparent that these insects ex- 
hibited a number of striking similarities. When the sim- 
ilarity of the wings was noticed, a comparison of other 
body structures seemed desirable. Since these could not 
be studied in the fossils, it was necessary to turn instead 
to the Plecoptera, in the hope that additional resemblances 
could be found. Such resemblances have been observed, 
particularly in the sternal region of the thorax, and in 
the wing articulation; these are discussed briefly below. 
The Sialidae are extremely archaic insects; the venation 
has undergone but little change since the Permian. There 
are some specializations — fusion of MP and CuA in the 
fore wing, reduction of the anal fan, and lack of nygmata — 
but in structure and arrangement of the veins the wing 
remains primitive. No other living insect group shares 
with the Protoperlaria so many morphological features of 
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