— 236 — 
in view of the very wide dispersal of the species as recognized in 
the last quarter century, it is at least possible that we must consider 
it as a comparatively recent introduction. Of course the species has 
been recognized as far north as in Alaska, and itis possible that the 
point of invasion and dispersal has been from that quarter. 
Other cases of interest are to be found in the genera Scapho:- 
deus and Agallia. In Scaphoideus the species are practically all 
American, and until recently it was supposed to be strictly Amer- 
ican. The species occur all the way from the Boreal zone to the 
Tropics, but the majority are known from the Transition or Austral 
region. The Exotic species so far as observed occur in Japan, 
India and Egypt. For this genus it would appear therefore that 
the center of origin was in the central or southern United States, 
and that the lines of dispersal have been to the north and south, 
and especially northwest for the extension to the Palearctic region. 
For Agallia the origin of the group appears rather to have been 
tropical, possibly an old-world species, and the lines of distribution 
into south and central America and thence northward The 
northern limits for the species for the most part are coincident with 
the Transition or Boreal zone. 
Both Athysanus and Deltocephalus are well represented in 
North America, and a number of the species show great adapt- 
ation for conditions in the central plain and desert region of the 
United States. Both have evidently been represented in the region 
for a long period, and it is quite possible, at least for the latter, 
that the center of dispersal was from this region. For the grasses 
of the plain and desert there has been a remarkable modific- 
ation, in some cases the development of distinct dimorphic forms 
and a definite restriction to certain species of plants. 
The genus Dorycephalus is represented in the central northern 
part of the United States, and species here apparently parallel the 
only other known species which occurs in Russia in their adaptation 
to particular grasses, and to a dry climate. Our species have a 
remakable adaptation to the plants on which they live, the larval 
forms presenting very striking cases of resemblance to certain parts 
of the plants. 
On the whole it may probably be said that the Jassidæ have 
had more or less of their development in both of the regions, 
but that considerable number of the genera quite certainly had 
their evolution in North America, and their dispersal to adjacent 
countries. 
