THE CLASSIFICATION OK THE BROODS. 21 
taken except three, which he supposed would be filled when the 
region west of the Rocky Mountains became known, and lie gives the 
distribution of twenty-one broods by State and counties, classified 
according' to races, substantially as subsequently listed by Profe 
Riley. 1 Dr. Asa Fitch introduced a numbering system for the different 
broods, recording nine altogether: but his data on the distribution of 
the species and of the several broods was very limited and altogether 
inadequate to make an accurate survey of the field possible. Our 
present understanding of the broods in this country is substantially 
that given by Professor Riley in 1869, which supplanted the Walsh- 
Riley enumeration of the year before, and is based in part on Dr. 
Smith's manuscript and on the abundant data and information which 
Walsh and Riley collected in 1868, when the joint occurrence of the 
two largest broods, respectively, of the 17-year and 13-year races, gave 
especially favorable opportunity for study and historical research. In 
this catalogue an entirely new set of numbers was given to the broods. 
This was necessitated by the fact that the earlier writers, with the 
exception of Dr. Phares and Dr. Smith, were unaware of the existence 
of the Southern 13-year race, and necessarily much confusion of broods 
resulted. Of the twenty-two broods enumerated by Dr. Riley in lSb9, 
subsequent observations have established the validity of twenty-one, 
fourteen belonging to the 17-year race and seven to the 13-year race. 
These broods vary enormously in their extent, some of them being 
represented by scattered colonies, which perhaps have no real relation- 
ship in point of origin, and others covering nearly uniformly vast 
stretches of territory extending over several States together. 
The broods to the number of twenty-one, the facts concerning the dis- 
tribution and appearance of which are well ascertained, do not n< 
sarily include all of the broods of the Cicada which actually occur on 
this continent. The scattering examples of this insect which, while 
very few in number, sometimes appear on other than Cicada years may 
be explained either on the ground of acceleration or retardation of 
individuals belonging to regular broods or as representing small or 
insignificant broods which have not been recognized as such and may 
be either broods in the process of formation or of extinction. A brood 
which perhaps comes under this category was recorded by Prof. .1. A. 
Lintner in his seventh report (pp. 1*97—301 and was represented by 
scattering individuals of the periodical Cicada appearing at Tivoli. 
N. V., in June. 1890. In a letter to Dr. Lintner, Professor Riley, refer- 
ring to this occurrence says: " 1 agree with you that the Tivoli Cicada 
<an not be referred to Brood VI II. and if they were numerous enough 
to be called a brood they would form one hitherto unrecorded." He 
mentions also some additional records in his possession "of new or 
doubtful broods,*' and concludes: k - It is safe to say that we know now 
pretty accurately all the large broods of the periodical Cicada, but it 
See Appendix C, 
