6 THE PERIODICAL CICADA. 
It so happened that one of the largest 17-year broods, together with 
one of the largest 15-year broods, appeared simultaneously in the sum- 
mer of 1868. Such an event, so far as regards these two particular 
broods, had not taken place since the year 1647, nor will it take place 
again till the year 2089. 
There are absolutely no perceptible specific differences between the 
17-year and the 13-year broods, other than in the time of maturing ; but 
while the insects forming these two classes of broods are not specifically 
distinct, they are good and distinct races which do not cross, and I 
have therefore, for convenience sake, named the 13-year broods Cicada 
tredecim. 
TWO DISTINCT FORMS. 
It is not a little singular, also, that two distinct forms occur in both 
races—a large one and a small one—the former by far more numerous 
than the latter. This fact has been observed in past years, and was 
Fic. 1.—Seventeen-year Cicada. A, ¢ of typical form; 
ce, d, genital hooks; g, singing apparatus. Bb, ¢% of the 
small form (cassinii); e, f, genital hooks. (After Ri- 
ley and Hagen.) 
noticed in 1868 by independent observers in different parts of the 
country.* Indeed, it was observed by Dr. Hildreth, of Marietta, Ohio, 
as far back as 1830 (vide Silliman’s Journal, XVIII, p. 47). The true 
Cicada septendecim of Linnzus (Fig. 1 A, ventral view of male), as 
as early as May 17, 1845, where he controverted Dr. Smith’s position to the effect that 
there were no 13-year broods; and that in the same paper, for May 5, 1858, he pub- 
lished another notice, headed ‘‘Cicada Tredecim.” It was not till 1873 that I became 
aware of these facts though I had previously been in correspondence with Dr. Phares ; 
and though I have made every effort since to obtain a copy of the original article 
to which Dr. Phares refers, both he and myself have utterly failed to do so. While, 
therefore, it appears that Dr. Phares has trusted to memory for the dates here given, 
there is no reason to doubt the essential accuracy of the facts, and that to him rather 
than to Dr. Smith belongs the discovery of one of the 13-year broods of this Cicada, 
and the credit of having first published the fact. 
*1. Mr. V. T. Chambers, in the August (1863) number of the American Naturalist, p. 
332, is said to point out some variation in color from those described by Dr. Fitch. 
2. Mr. S. S. Rathvon favored me with specimens of both species from Lancaster 
