32 THE PERIODICAL CICADA. 
negative and positive. Reports were also kindly submitted Ijy 
Professor Forbes, of Illinois, which added four or five counties to 
the records obtained for that State, and other reports were received 
from entomologists of other States covered by this l)rood. A })re- 
limmary report was published in Bulletin 14, and a full report in 
Bulletin 18, of this Bureau. The records obtained confirmed the 
general accuracy of the old belief of the distribution of Brood XXIII. 
The occurrence of scattering colonies of the 17-year Brood VI over 
some of the territory adds a slight element of doubt; but in the 
main the records given for Brood XXIII, taken in comiection with 
older records, are probabty correctly assigned. 
The data obtained of the 17-year Brood X in 1902 is even more 
satisfactory, inasnmch as in this case there was no 13-year brood to 
throw doubt on any of the records. The same means was taken to 
get full reports as were used in 1898; and, rather to our surprise, the 
substantial correctness of the old records is strikingly demonstrated, 
as seen on the map published in connection with the detailed discus- 
sion of this brood. Thirteen-^^ear Brood XXIII covers southern 
Illinois, with a scattermg outpost through southern Indiana. Brood 
X stops, as hitherto believed, near the eastern line of Illinois, with 
a few scattering outposts. There is overlappmg, but, in the mahi, 
south-central and western Illinois and eastern and central -^lissouri 
seem to belong to the 13-year race, as hitherto believed. 
The recurrence this 3^ear of the great 13-year Brood XIX without 
any 17-year brood to confuse the records will give an opportunity 
to complete the data relative to the distribution of these three over- 
lapping broods, but the records already obtained of Broods X and 
XXIII indicate very strongly the probable correctness of the old 
records of Brood XIX. 
Many of the other scattering records of 13-3'ear broods northward, 
or of 17-3"ear broods southward, may possibh^ be based on similar con- 
fusions, arising from the overlapping of broods of the two races. 
The only way to accurately defme the range of the different broods 
is to undertake with each recurrence a thorough and systematic 
investigation of all the territory open to the least doubt. Such work 
has been repeatedly instituted, and particularly since 1868, and many 
of the more strictly limited broods have been very carefully recorded, 
and their distribution has been satisfactorily defmed. Work of this 
kind has been done for Brood III in Iowa by Professor Bessey, and 
for Brood V in Ohio and West Virginia by Professors Webster and 
Hopkins. Similar work has been done for Brood II in Xew York 
and New Jersey by Doctors Lintner and Smith, and for X and XXIII 
by Riley m 1885, and for Brood XIX by Walsh and Riley m 1868. 
