62 ENTOMOLOGICAL NEWS [Feb., '15 



instance observed may account for the fact that no orange 

 females have been seen ovipositing in the field. The fact that 

 the pruinose orange female assumes with age the deeper color- 

 ation of the so-called black one, would naturally make this 

 latter form far more numerous in the fall. 



BIBLIOGRAPHY. 



1893 CALVERT, P. P. Catalogue of the Odonata (Dragonflies) of the 

 Vicinity of Philadelphia. Trans. Amer. Ent. Soc. XX, pp. 

 152-272. 



1899 NEEDHAM, J. G. Directions for Collecting and Rearing Dragon 



Flies, Stone Flies and May Flies. Bull. U. S. Nat. Mus., No. 

 39, Ft. O. 9 pp. 



1903 NEEDHAM, J. G. Aquatic Insects in New York State. Bull. 

 N. Y. State Mus., 68, pp. 218-279. 



1900 WILLIAMSON, E. B. The Dragonflies of Indiana. Geol. Surv. 



Indiana Kept., pp. 229-333. 7 pis. 



THE DIMORPHISM OR DICHROMATISM OF THE FEMALES OF 



ISCHNURA VERTICALIS. 

 By PHILIP P. CALVERT, University of Pennsylvania, Philadelphia, Pa. 



Of the authors who have written on the females of Ischtutra 

 verticalis, I believe that only Calvert (1893) and Williamson 

 (1900), both in part only, Ris (1903) and Walker (1908) 

 have correctly recognized the true dimorphism which exists 

 in this sex in individuals of the same age. The two forms 

 recognized by others are not forms of equal age, but color dif- 

 ferences due to age. Miss Lyon, in her preceding paper, has 

 shown that the orange female becomes pruinose and black, 

 but I think that she has experimented with but one form of 

 female to be found in this and other species of Ischnnra, that 

 which in treating of the genus, in the Biologia C entrali- Ameri- 

 cana, I called the hetcro chromatic female, as being colored un- 

 like the male. 



The two true dimorphic or dichromatic forms are only to be 

 recognized with certainty when the student has teneral, or rela- 

 tively recently emerged, females before him. Their differ- 

 ences may be most concisely shown in a table: 



