18 
Psyche 
[March 
faunas, we even find genera which were first known to us 
only as fossils and supposed to have been extinct. Such a 
genus is Archipsocus, described by Hagen for an amber 
Psocid, but subsequently found to be existing in the tropics 
of both the New and the Old World. Another instance is 
the ant Gesomyrmex, which was originally described by 
Mayr from the amber, and which was found many years 
later in the region of Borneo. 
Now if we go back another hundred million years on the 
geological calendar, to the Middle Mesozoic, we are unable 
to recognize definitely any existing genera, but we do find 
many families quite familiar to us at the present time. Of 
course, as one would naturally expect, there is a marked 
difference in the development of the several orders. All the 
Mesozoic Trichoptera, for example, belong to extinct fami- 
lies, but many of the Orthoptera and Diptera can be in- 
cluded within modern families. When we reach the Permian, 
another 50 million years away, we observe that our recent 
families no longer make their appearance, but we are still 
able to recognize several existing orders, as the Mecoptera, 
Neuroptera, Odonata, Diptera, etc., including types with 
complete metamorphosis. However, receding another 50 
million years — making a total of about 250 million — we 
come to the Upper Carboniferous, in which our earliest 
winged insects have been found. Here we find an assem- 
blage quite unlike that of any other period, including such 
primitive forms as the Paleodictyoptera, and a few more 
highly specialized groups as the Protodonata and Megase- 
coptera. Only one recent order, Blattaria, has been rec- 
ognized without question in the Upper Carboniferous 5 . 
Tillyard has described from even older rocks, the Devonian 
of Scotland, the remains of some arthropods which he con- 
siders to be true Collembola, but I do not believe that ento- 
mologists in general have accepted his conclusions. The 
absence of winged insects from strata below the Upper 
Carboniferous is particularly disconcerting, for, primitive 
as these coal measure insects may be, they are nevertheless 
5 Tillyard maintains that the obscure Metropator imsilws Handl., 
from the Pottsville series of the Upper Carboniferous, is a true Mecop- 
teran, but this is very dubious. See G. C. Crainpton’s discussion, 
Psyche, 37, 1930; p. 93. 
