132 Annals Entomological Society of America [Vol. VIII, 
only to these land connections, but to the varying places of 
origin of the various families and genera. Of the insects in any 
country, some are endemic, some ancient migrants, some more 
recent migrants. 
Our western Raphidiid fauna, and absence of Panorpid 
fauna could be explained in two ways. The Raphidiudze may 
have arisen there and migrated to Asia during a land connection, 
or else if it came from Asia the genus Panorpa was not as 
abundant in Asia as at the present time. 
It will be seen from the foregoing that I consider the insect 
fauna of the United States to be composed of several elements. 
I believe there are at least five that can easily be distinguished. 
1. Genera which are relicts of a very ancient fauna when 
land masses were of a different conformation from now. These 
genera are isolated in our fauna and mostly examples of discon- 
tinuous distribution. 
One of these series includes the Panorpodes, the Hypochilus, 
Lachnocrepis, Pristodactyla, Tachopteryx, Hagenius, Tmestphorus, 
Midea (section of Anthocharis), Cryptocercus, of the Alleghanian 
fauna, and doubtlessmany other forms showing relation of Cali- 
fornian and northwest with Europe or Siberia and Japan. Such 
are Raphidia and Megalomus in Neuroptera. Paraplinthus and 
Necrophilus are apparently also in this series, and probably 
Amphizoa and Cephaloon, perhaps Rhinomacer. 
In Southern California there is a series of isolated genera 
which indicate relationship to a very ancient fauna, perhaps 
connected to the islands of the South Seas. Such are 
Dinapate, Distaxia, Schizopus (Coleopt.), Oliarces (Neur.), 
Hubbardia (Arachn.), Timena (Orth.), probably Apioceride 
(Dipt.), and the true Thynnide (Hym.), also belong to this 
group, which stands widely apart from the other insects 
around it. 
In this section we might include any descendants from our 
Paleozoic insects; I doubt if it is possible to trace any such 
genera, but our curious Merope tuber may be such a form. 
The Sialidae may have arisen within our territory as descendants 
from Paleozoic forms, but from their present distribution one 
would suspect Southeastern Asia as their starting place. Our 
mayflies are probably later migrations; Pteronarcys in Perlide 
may be a derivative of that ancient fauna, but I doubt 
it; our cockroach fauna is also probably due to later migrations. 
