NO. 2192. DRAG0NFLIE8, CALIFORNIA AND NEVADA— KENNEDY. 567 



Doctor Needham * as confratemus, are close to the nymphs of donneri 

 but are slightly broader. 



In color this species is characterized and set oflf from sohrinus by 

 the narrow antehmneral stripes (1 mm.), the solid black humeral 

 stripe, the minute lateral spots on segments 4-7, the usual absence 

 of a dorsal spot on segment 9, and the fact that the lateral spot of 

 segment 9 never quite reaches the lower posterior angle of the seg- 

 ment. (See figs. 306-308.) 



Structurally the species is characterized by its shorter pterostigma 

 (2.5-3.2 mm.), by its more slender abdomen and by its more blunt 

 superior appendages and slightly lyrate inferior appendage. 



This species is veiy close to sohrinus, differing from it in the above 

 characters and in its season. The season of sohrinus is entirely past 

 before this reaches its prime. The difference in altitude would 

 account for part of this, but hardly for so great a difference. And 

 as to the characters above, none of them are constant except that 

 of the extent of the yellow lateral spot of segment 9. In sohrinus 

 it always attains the posterior angle and in donneri it never does. 

 Occasional specimens show mtergradations in any of the other char- 

 acters, but no single specimen from the valley (sohrinus) or from the 

 lake (donneri) shows a major part of its characters varying toward 

 the other species. 



To test this I tabulated each specimen of the males of the two 

 species (54 donneri and 50 sohrinus) in regard to the following seven 

 characters: 1, width of pale antehmneral stripe; 2, length of pale mid- 

 humeral stripe; 3, length of stigma of left forewing; 4, extent of 

 lateral spot of segment 9 along the inferior edge of the segment; 

 5, length of dorsal spot on segment 9; 6, character of superior appen- 

 dages (whether needle pointed sohrinus form or the blunt donneri 

 form or one of three intermediate forms) ; 7, character of inferior 

 appendage. The table (see p. 568, table A) following shows the varia- 

 tions and the number of specimens showing any given variation. The 

 arrangement of the table brings out the overlapping or intergrading 

 of the various characters. 



To show the distinctness of the two groups of dragonflies in spite 

 of the intergrading of the various characters, I reduced the measure 

 of each character to its equivalent in a scale of ten, allowmg for 

 the extreme donneri form of each character and 10 for the extreme 

 sohrinus form of each character. The equivalents for each character 

 are inserted in the table of variations. 



Following this (see p. 568, table B) are for example the measure- 

 ments of the first three donneri specimens and following each in the 

 table are inserted the equivalents for that specimen with their suu ^n 

 the end column. 



1 Proc. U. S. Nat. Mus., vol. 27, 190-1, p. 691. 



