484 



CALIFORNIA ACADEMY OF SCIENCES. 



As a matter of practice, the writer has found it con- 

 venient to paraphrase these two characterizations in this 



I. Postcostal vein separating from the hind margin of the wing* at 

 least as far in front of the basal postcostal cross-vein as the latter is long. 



II. Postcostal vein separating from the hind margin of the wing at the 

 basal postcostal cross-vein or at less distance in front than the latter is 

 long. 



The genus Erythragrion Selys belongs to the second 

 of these two sections. It having been noticed that the 

 specimens from Baja CaHfornia varied with respect to 

 the point of separation of the postcostal vein, the varia- 

 tions were carefully tabulated, as shown below, together 

 with some other species for comparison. The table 

 refers to the front wings only. 



Name of Species. 



Erythragrion salvum. . . 



(Baja California.) 

 Erythrayriondominicanum 



(West Indies.) 

 Pyrrhosoma tenellum. . . 



(Europe.) 

 Pyrrhosoma mhiium . . . 



(Europe.) 



Number 



of 

 individ- 

 uals 

 exam- 

 ined. 



55 5 



r 



69 

 5? 

 8$ 



Postcostal vein separating from hind 

 margin of wing 



at least as 

 far in front 

 of basal 

 postcostal 

 cross-vein 

 as latter is 

 long 

 (Case A). 



in front of 

 basal post- 

 costal cross 

 vein at less 



distance 



than latter 



is long 



(Case B). 



18. 5 

 6? 



3$ 



5? 

 9$ 



7? 



29 S 



13? 



SS 



4? 

 1 S 



at the 

 basal 

 post- 

 costal 

 cross- 

 vein 

 (Ca5e C). 



3S 



1? 

 3$ 



1? 



Case A 

 in one 

 front 

 wing. 

 Case B 

 in the 

 other. 



5$ 

 2? 



1? 



Case A 

 in one 

 front 

 wing, 

 Case C 

 in the 

 other. 



2S 

 1? 



It thus appears that in the case of jS". salvum from 

 Baja California, 32.7 per cent, of the males and 27.3 per 



*0n the preference for this form of expression see Trans. Am. Ent. Soc. 

 XX, p. 164 at bottom. 



