1915] Distribution of Neuropteroid Insects 27 
Since the main orders of insects have existed on this earth 
the gross outlines of continents have changed several times, and 
between these changes there were migrations and dispersals, just 
as there is today. So that today each continent has insects 
which by their structure and origin are isolated from the other 
insects around them and find their relations only to insects of 
distant countries. 
The striking cases of discontinuous distribution have to me 
a most significant importance; I hardly think that their value 
has ever been sufficiently appreciated by the student of 
geographic distribution. 
A few years ago I stood in an isolated valley in Western 
North Carolina. About me were flying several species of 
Panorpa and a Bittacus, Panorpids which are widely distributed 
in the Eastern United States, not one of which occurs in the 
Western States. Yet right with these Panorpids was another, 
a species of Panorpodes, a genus whose only other known habitat 
is Oregon and Japan. In that same valley are many spiders, 
nearly all of which are common over much of the Eastern United 
States, but yet there, and in several nearby places in the South- 
ern Appalachians, is a curious spider, Hypochilus. Where else 
does it occur? In Colorado, and a closely allied genus in North 
China, and one in New Zealand. Hypochilus, and its related 
genera are the only known members of what is structurally the 
most isolated family of spiders. Panorpodes is also a very dis- 
tinct genus and less specialized than the other Panorpid genera 
around it. 
These two cases are but samples of a long list of insects (and 
also plants) that show a relationship of our Alleghanies with the 
Northwest, and with Japan and North China. How did it 
happen? I doubt if-you can find a single genus of insects which 
is now known only from the Southern Appalachians and say 
from Eastern Brazil, or West Africa; regions no more distant 
than Japan. Why are there not such cases? 
Consider another series of cases. In Eastern South America, 
in Argentine, and parts of the Andean region there are several 
species of a genus of handsome antlion flies, Dimares. It is 
structurally very unlike anything else in South America. Yet 
in South Africa, in Arabia, in Ceylon are species of another 
genus Echihromyrmex, so similar to Dimares, that one is loathe 
