FUTURE APPEARANCES. 23 
and Wisconsin. The colonies reported as occurring on tlie northern 
slope of the Big Horn Mountains of Montana and Wyoming are prob- 
ably based on a confusion of this with some other species of Cicada. 
The distributions of Broods XVII and VII is shown in fig. 4. ] 
FUTURE APPEARANCES. 
During the next seventeen years broods of the 17-year and 13-year 
races of the periodical Cicada will occur as follows: 
Table of future appearances. 
17 /£ ar 
1898 ' XVII 
1899 XIX 
1900 XX 
1901 j XXI 
1902 j XXII 
1903 1 I 
1904 1 
1905 V 
1906 VIII 
13-year 
race. 
VII 
Tear. 17 - v,ar r: -- vt5i,r 
race. race. 
XVI 
1907 
1908 
T X 
1909 -. .-- 
1910 
XI 
1911 
XII 
1912 
XIII 
1913 
XIV 
1914 
XV 
1915 ... 
XVII 
XVIII 
II 
IV 
VI 
VII 
It will be noticed that, as a rule, a 17-year race and a 13-year race are 
associated in the same year. This is purely accidental, and in point 
of fact the same two broods could only come together at very long 
intervals of time. Taken as a time measure, the recurrence of a* joint 
appearance of any one of the 17-year with any one of the 13-year broods 
furnishes a very long yardstick in years. For the return the same year 
of two such broods a lapse of more than two centuries is necessary. 
For example: The great Cicada year of 1868 will not be duplicated 
again by the joint recurrence of the same broods until the year L'OSO, 
when perhaps the increase of settlement and the changed character of 
vegetation and superficial conditions over their respective ranges may 
have entirely eliminated them, except for stragglers. The broods which 
unite in time of appearance the present year were last in conjunction 
in 1G97 and will not again come together until the year 2119. 
THE DISTRIBUTION OF THE PERIODICAL CICADA. 
SOURCES OF INFORMATION. 
In explanation of the matter contained in this section, it should be 
stated that in the original plan it was intended that Mr. B, A. Schwarz, 
who had long assisted Professor Riley in collecting the data relative 
to the distribution of the broods of the Cicada, should prepare a full 
account of all the known broods, detailing the chronological records 
1 The records of occurrence for 1898, obtained while this bulletin was going through 
the press, are numerous, and are summarized in Appendix 1>, p. 111!. 
