1930 ] 
Geological History of Insects 
19 
perfectly respectable insects and so far along the line of the 
Insecta that they show no definite relationship with other 
Arthropods. 
With this general survey of insect paleontology in mind, 
I suggest that we now examine more carefully the geological 
ranges of the larger and more prominent insect orders. Of 
the extinct ones certainly the most interesting, phylo- 
genetically, is the Paleodictyoptera. These generalized cre- 
atures, which are usually regarded as the ancestors of all 
the other winged groups, were developed into many diver- 
sified families before the end of the Carboniferous; but for 
some reason their glory was brought to an abrupt end, for 
only one species is known to have persisted into the Per- 
mian. Another interesting Carboniferous order was the 
Megasecoptera, the members of which were unique among 
the other known species of the period in that they possessed 
petiolate wings, not very much unlike those of the damsel- 
flies. These insects appear to have completely died out be- 
fore the Permian, but some recent groups are supposed to 
be their direct descendants, — as the Odonata and Mecop- 
tera. The order Protodonata, another assemblage which has 
never been found living, is especially famous because of the 
large size attained by some of its members, Meganeura of 
the Commentry of France having a wing-expanse of about 
29 inches. This order, in contrast to the foregoing, 
persisted through the Permian, but apparently became ex- 
tinct during the Triassic. All the rest of the Carboniferous 
insects, excluding a few very small orders with obscure 
affinities, seem to fall into what we may call the Blattoid, or 
cockroach, complex. Handlirsch and others have attempted 
to divide them into separate orders, such as the Protorthop- 
tera and Protoblattaria, but these groups overlap in many 
respects. This complex, in my opinion, represents the con- 
verging branches which later lead to several distinct orders 
of insects; it represents, in other words, the trunk of the 
conventional phylogenetic tree, where the several branches 
had joined — or were in the act of joining — into one. I sus- 
pect that as more and more Upper Carboniferous insects 
are found this complex will become even more jumbled; and 
I also believe that when Lower Carboniferous insects are 
discovered, as they eventually must, we shall find the Paleo- 
