3IO ENTOMOLOGICAL NEWS [July, '13 



dividual forms or "sports." Unfortunately we meet 

 quite often still with the old view that the naming of "aber- 

 rations, mutations," etc., is of no value. In opposition to this 

 view I wish to say that we know a species only, if we are 

 acquainted with all of its forms and their causes. In order to 

 make all the forms known and to separate them from each 

 other it is necessary to mark them in some way. Since, how- 

 ever, a designation of forms by letters or numbers cannot be 

 carried out, we are obliged to give them names. Of course it 

 is necessary only to characterize the extremes of each varia- 

 tion. Transition forms hardly need special names, or only in 

 exceptional cases, as, for instance, for defining forms which 

 develop at certain temperatures or for other definite causes. 

 The figures on Plate X are a little less than natural size 

 and a shade too light. 



The Species of Nehalennia (Odonata), 



Including one from the eastern United States hitherto undescribed. 



By PHILIP P. CALVERT, Ph.D., 

 University of Pennsylvania, Philadelphia, Pa. 



The genus Nehalennia was established by de Selys in 1850 

 for the European Agrion specwsum Charp. In his synopsis 

 of the legion Agrion in 1876 he included within Nehalennia 

 the following seven species: atrinuchalis Selys (Shanghai), 

 speciosa Charp. (Europe), Irene Hagen (United States), 

 sophia Selys, 1876 (Province of Minas, Brazil), posita Hagen 

 (United States), denticollis Burm. (Mexico), and lais Selys 

 (Mexico). In 1895 Morse described N. gracilis from Massa- 

 chusetts. Calvert removed denticollis to Ischnwa Charp. in 

 1898 and lais to Anisagrion Selys in 1902. In 1903 Needham 

 transferred \posita to Ischnwa. Five described species thus 

 remain in Nehalennia. References to the literature are given 

 in the catalogues of Kirby and of Muttkowski. Dr. E. M. 

 Walker has just published the differentials of the larvae of 

 N. irene and gracilis* 



*Can. Ent., XLV, p. 61, pi. I, figs. 1-3. June, 1913. 



