3 2 6 
The Ohio Naturalist. 
[Vol. Ill, No. 2 , 
There is, so far as I can learn, no positive evidence that the 
variety is a dimorph, which may reproduce the normal type, or 
that alternates with it. It is certainly not a sexual dimorph, as 
both sexes are represented in each form, and, as shown, else- 
where, pair by themselves ; seasonal dimorphism is evidently not 
to be considered, so that I see no reason to use the term 
“dimorphic” as applied to this species. 
The fact that the two forms appear simultaneously in the 
seventeen-year period and have so main- characters in common is 
certainly good evidence of a very close relationship, and it would 
seem safe to say that they have sprung from a common stock, or 
very likely* that one is a derivative from the other, which still 
represents the ancestral form. While not yet determined, it 
would seem pretty evident that cassini is the derived form, since 
it appears less commonly than the other and has probably a more 
restricted range. If, possibly, a depauperate variety, it seems 
now to be fully established as a distinct form. It pertains espe- 
cially to the brood XXII having such wide range the present 
season (1902), and was noted especially by Riley for the same 
brood in 1868. 
In my own experience it has been very rare in broods V and 
XIII, which I have had good opportunities to observe in Iowa in 
the occurrences of 1878, 1888 and 1895. 
Summarizing : (1.) There is a very constant color difference. 
(2.) Measurements show very close adherence to two entirely 
different averages for length of body, length of wing and width 
of wing. This is best shown by curves. (3.) There is a totally 
different note characteristic of each form, which must be consid- 
ered as representing different morphology of sound-producing 
organs as well as basis for selection of mates. (4.) No cassini 
forms have been found paired with normal forms and none have 
been recorded or reported by other observers. (5.) There is a 
difference in genitalia, though perhaps not enough to exclude the 
possibly of mating, and Riley says the differences are not con- 
stant. 
Whether this form be called a variety, sub-species or species, 
is, it seems to me, of less importance than a recognition of its 
distinctness, and a determination, if possible, of its phylogenetic 
relationship. For purposes of designation it may conveniently 
be called Tibicen cassini Fisher. 
A variation of a quite different type was noted, but was repre- 
sented by only two specimens. 
I am under obligation to Max W. Morse for assistance in 
making the measurements. 
