326 The Ohio Naturalist. [Vol. Ill, No. 2, 



There is. so far as I can learn, uo 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-}-ear period and have so many characters in common is 

 certainl_y good evidence of a very close relationship, and it would 

 .seem safe to sa^- that they have sprung from a connnon stock, or 

 verj' 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 cass//i/ is the derived form, since 

 it appears less commonly than the other and has probabh- a more 

 restricted range. If, possibly, a depauperate variet}', it seems 

 now to be full}' 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 b}- Riley for the same 

 brood in 1868. 



In m}' 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 : ( i.) There is a ver\' constant color difference. 

 (2.) Measurements show very close adherence to two entirel}^ 

 different a\-erages for length of bod}-, 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 nuist l)e consid- 

 ered as representing different mor2:)hology of sovuid-producing 

 organs as well as basis for .selection of mates. (4.) No rassmi 

 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 

 possibl}- 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 Tibiccn cassini Fisher. 



A variation of a quite different type was noted, but was repre- 

 sented In' only two specimens. 



I am under obligation to Max W. Morse for assistance in 

 making the. measurements. 



