BOUNDARY OF PERMANENT REGION. 
them from A. americamim and agreeing exactly with that of the former 
species. 
Mr. E. Flint, in his letter of December 18, 1877, speaking of the migra- 
tory locusts that visit Nicaragua, says : "They resemble (Edipoda Say y 
these have spotted elytra wings, and are larger; last ventral segment 
notched, as in spretusP 157 
According to his letter specimens were sent to the Smithsonian Insti- 
tution for determination, but we cannot learn that they were ever re- 
ceived.* We think it almost certain that the species does not belong to 
the genus (Edipoda, or to the group (Edipodini. It is most probably an 
Acridium, either A. americamim or a closely allied species ; the " spotted 
elytra" and notch in the last ventral segment agree with this supposi- 
tion, the prominent notch in the male of this species being readily ob- 
served. In addition to this we may say that large (Edipodce appear to 
be very rare in Southern Mexico and Central America, while in this re- 
gion and the northern part of South America Acridium reaches the 
maximum in development. A small collection made last summer in 
Central America by Professor Burrill contained but a single CEdipodean. 
These reasons, we think, are sufficient to render it more than prob- 
able that the Eocky Mountain locust does not extend its incursions into 
Mexico or Central America. 
The line on map No. 1, marking the outer limits of its distribution as 
given in our former report, may be considered as very nearly correct, 
requiring no change, perhaps, except at one point. Facts ascertained 
during the past and present season indicate a more southern extension 
in New Mexico, and possibly in Arizona. We have, then, an area ex- 
tending east and west from the 93° to 119° of west longitude and north 
and south from 27° to 53° of north latitude ; or 26° east and west and 
26° north and south, which has as its strongly marked features an im- 
mense and highly elevated plateau from which shoot up sharp ranges and 
lofty peaks. This elevated section is bordered by broad, treeless plains ; 
the entire area is to a large extent free from forests, the chief exceptions 
being the higher mountain masses in Colorado and Wyoming, and the 
mountainous section in West Montana. Not only is this vast area, taken 
as a whole, comparatively treeless and barren, but the climate is dry, 
the average rainfall not exceeding twelve or fourteen inches per annum. 
By comparing the area of distribution of this species with that of 
other species, we are enabled to deduce some important laws in refer- 
ence to locust distribution, and the laws of migration which cannot be 
detected by studying one species alone. 
The paper by Mr. F. T. Koppen in Petermann's "Mittheilungen aus 
Justus Perthes' Geographischer Anstalt," in regard to the distribution 
of Pacliytylus migratorius has already been referred to in our former re- 
port, and M. Preudhomme de Borre's brief analysis of it is given there. 
According to this the northern limit of the permanent distribution of 
167 See former Report, p. 465. 
* Kote. — Specimens, possibly of this collection, sent us are closely allied to A. peregrinum. 
