26 THE PERIODICAL CICADA. 
Walsh-Riley enumeration of 1878 gave the records for sixteen broods, 
which were designated by Roman numerals from I to XVI, the enumer- 
ation being based on the sequence of the different broods after 1868. 
In 1869, in his First Missouri Report, Professor Riley, having in the 
meantime secured the manuscript paper of Doctor Smith, added the 
six broods from this paper not represented in the Walsh-Riley enu- 
meration, increasing the number of the broods to XXII, and renum- 
bered them again in: accordance with their sequence, beginning with 
1869. ‘These broods vary enormously in their extent, some of them 
being represented by scattered colonies, which perhaps have no real 
relationship in point of origin, and others covering nearly uniformly 
vast stretches of territory extending over several States together. 
Several are rather unimportant, or lack confirmation, and one of 
them, Brood III, was founded on an erroneous record and has been 
dropped. 
In the enumeration of the broods by Walsh-Riley, and later by 
Riley, the two races are mixed together and a sequence of numbers 
given which, after the first thirteen years, lost all significance as a 
record of the order of the broods in time of appearance, and from 
the first obscured the true kinship of the broods in each race. If, on 
the other hand, each race be considered separately and its broods be 
arranged in a series in accordance with their sequence in time, an 
important natural relationship in point of origin and distribution is 
plainly indicated. 
Taking first the broods of the 17-year race, as Riley numbered them, 
it will be seen from the subjoined table that if the enumeration begin 
with Brood XJ, the 17-year broods follow each other in regular succes- 
sion for eleven consecutive years, then after a break of one year fol- 
low Broods V and VIII, and after another break of one year Brood 
IX. Another break of one year precedes the next recurrence of Brood 
XI, with which the series starts. 
Chronological order of the Riley broods of the Cicada from 1898 to 1910. 
pe 17-year | 13-year | rx 17-year | 13-year 
Year race. | race. | Year. race. race. 
| 
ROSIE AR os ee ee pane ten FS eee SL | ese Val 1902s 1 Cee Sek eae | “OREN Tiy sees 
TRO Dies Soe ed ae ne SEL LO NEWAITE 11/1 G O30 sere he nn renga i eR ES 
II 2 5 aed ae ee ee Oa S| II NODAL RRs Et ah lesion 22 a | ees 
SOG eso io te ops Yen a tees XIV 1\ | ROS tee. ke. ee amie Vee 
Ihe tS ee eee ees eee | eee aoy Wali UN GOGSS 1-5. et Se eee On ee VII |) evil 
ISOS BEN Se tans eee eee XVII VII LOOT 2,222 Shas Eel ake arte, ae ee | XVIII 
S99 S Ca wae aaa ces Se XGA |e Pee 19082 2) Rees se | Ix I 
1 Oe See Seer mee wate eser Ke Se Se eel 1909. Bar Rock sc ae eoe oe Ae EE Renee ae IV 
LOD IME AD. Cael Baia co eee ae AIS lhe x TOL OLA: Pe Swi ae ew | a VI 
Taking up the 13-year broods in the same way, it will be seen that 
if the enumeration start with Brood XVI, a 13-year brood follows in 
regular succession for six years. With the exception of the very 
doubtful Brood X, which is separated from the last 13-year brood by 
