58 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
more restricted area within the limits of their migrations, our first step 
in trying to fix the boundaries of this area for 0. spretus was to deter- 
mine as nearly as possible the outer limits of its geographical distribu- 
tion. This was not difficult, except where the line runs through unin- 
habited sections from which no data could be obtained ; as this limit, so 
far as this species is concerned, is determined not by straggling indi- 
viduals, but by the utmost points to which flying swarms reach, for 
beyond these points stray individuals are seldom seen. 
This outer limit of geographical distribution is found marked in map 
No. 1 of our former report, which is repeated in the present volume. 
The southern limit, which is supposed to pass through New Mexico and 
Arizona, has not been determined with satisfactory certainty, and it may 
be that, as mapped through Texas, it is slightly incorrect, as it is possi- 
ble that the species extends it's migrations into Eastern Mexico. It is 
even possible that the locust which occasionally devastates other parts 
of Mexico is Caloptenus spretus, but we think otherwise. We also know, 
from personal examination of specimens, that the species which occa- 
sionally overruns Honduras, the southern districts of Mexico, and Central 
America is quite distinct, and believe that the Eocky Mountain locust, 
with the exception of occasional visits to the southern side of the lower 
Kio Grande Valley, never goes south of the United States boundary. 
Our reasons for this opinion may be briefly stated as follows : The G. 
spretus is evidently, as we have shown in our former report, a boreal in- 
sect. We cannot learn that any of the collections of insects made in 
Mexico contain this species, and we have been unable to obtain any evi- 
dence of its being found in that country. So far as it is possible to 
judge in reference to the species, in the accounts of locust ravages in 
Mexico and Central America, they appear to differ from C. spretus. In 
the account given by Gage, in his "New Survey of West Indies," 154 it is 
stated "They were after the manner of our grasshoppers, but somewhat 
bigger;" also, that "where they lighted, either upon trees or standing 
corn, there nothing was expected but ruin," &c. The size indicated here 
is certainly larger than our Eocky Mountain locust ; and, secondly, the 
allusion to their alighting on trees is more applicable to the habit of 
Acridium americanum and its congeners than to C. spretus. The locust 
alluded to by Squiers 155 is evidently too large for our species, measuring, 
according to his statement, " two and a half to four inches." 
Those which have of recent years appeared in Yucatan are evidently 
species of Acridium. Some specimens were sent to Mr. S. H. Scudder, 
most of which proved to be A. americanum ; a few specimens were ob- 
served of an unknown species allied to A. flavofasciatum 156 . Specimens 
received during the past season from the West Indies, which give in- 
dubitable evidence of having migrated, cannot be distinguished from 
A. peregrinum, the ultimate segment of the male abdomen distinguishing 
164 See former Report, pp. 461-2. 
166 Quoted in our former Report, p. 460. 
166 See former Report, p. 462. 
