38 THE PERIODICAL CICADA, 
THE RANGE OF THE WELL-ESTABLISHED BROODS, TAKEN IN NUMERICAL 
ORDER. 
In the following description of the broods they are taken up in 
their numerical order—first, the 17-year broods, I to XVII, and then 
the 13-year broods, XVIII to XXX; that is, as many of the latter 
as have definite records. The chronological order of the broods, show- 
ing the broods of the two races which occur jointly in the same year, 
is indicated in the table on page 34. This arrangement, rather 
than a chronological one, is adopted for the reason that any chrono- 
logical arrangement in the course of a few years becomes obsolete, 
and for the same reason individual maps of the broods have been 
made, rather than joining in one map the two broods that may hap- 
pen to occur together on each of the next thirteen or seventeen years. 
The maps of important broods which have been recently more care- 
fully studied have been entirely revised, and the importance of the 
records has been indicated by the size of the dots, the large dots 
representing counties in which the brood occurred in one or more 
dense characteristic swarms and the small dots, records of scatter- 
ing occurrence or of doubtful validity. These same conditions are 
more accurately shown in the State and county records, as described 
under each brood. Such indications will be secured for all the broods 
in course of time, and will give a much more accurate picture of 
actual conditions than the old system of uniform dots for all records. 
The maps of broods which have not been recently studied have also 
been reengraved because of the discovery of new records—in some 
cases few in number, in other cases of considerable amount. 
Broods of the Seventeen- Year Race. 
Broopv I—Septendecim—1910. (Fig. 4.) 
Brood I is the first of the series of well-authenticated broods of 
the 17-year race, and its main swarms occupy the territory immedi- 
ately west of the more important Brood II, which follows the year 
after. It mecludes also widely separated swarms extending west into 
Kansas. It was established originally on data given by Dr. Gideon B. 
Smith, but its distribution is now more definitely recorded as a result 
of the study given it in 1893 by Professor Riley and of records which 
have come to this Bureau in connection with the study of other 
broods since that time. Several new counties for West Virginia 
were added by Doctor Hopkins in Bulletin 68, West Virginia Experi- 
ment Station (1900). 
The doubtful records prior to 1893 were those relating to the occur- 
rence of this brood in Kansas and Colorado. The localities in Kansas 
received doubtful confirmation in 1893. The Colorado localities 
remained unverified, although the district mentioned was visited 
