xxxiii, '22] ENTOMOLOGICAL NEWS 109 



This is a remnant of the preglacial fauna of Eurasia, so that 

 it lias no near relatives. It is remarkably specialized in the 

 penis which has a large inflated tip. Pontia, which Ris rates 

 as a variety, the writer has not seen. 



From the foregoing discussion the writer believes that thte 

 method of investigation as a preliminary to a study of the geo- 

 graphical distribution of a group of species is sound and fur- 

 nishes data as to relationships not easily arrived at from other 

 methods. The writer admits that he has used other characters 

 very little, though they agree as far as he has checked them. 

 To summarize : 



1. Scinifasciata is the most generalized living species and so 

 probably the most primitive. 



2. The genus LibcHitla originated in the eastern hemisphere 

 because there we find the large genus Orthctrnni, placed by 

 many writers close to Libcllula, in which the penis has the 

 straight lateral lobes of the less specialized Libellulas. See the 

 figure of an Orthctrnm penis in the preceding article, Ent. 

 News, vol. xxxiii, PI. II, fig. 14, 1922. 



3. Our southwestern species, sitbornata, foliata, nodisticta 

 and cowiposita, are the American species most nearly related to 

 the Eurasian Libellulas. This taken in connection with the 

 fact that the most primitive species, semifasciata, is in eastern 

 America, might mean that the genus originated in America 

 and spread to Eurasia, later sending northern species back to 

 America. 



4. These southwestern primitive species indicate a Mexico- 

 California faunal centre, which with its long unaltered climate 

 has been an asylum for various primitive Odonates, and from 

 which developed Group 4, Group 7 and Group 8. 



5. The species with broad lateral lobes comprised in Groups 

 3, 5, 6, 9 and 10 have probably been distributed to America 

 from Eurasia. This is indicated by the fact that their con- 

 necting links are not in America, that three of these, Group? 3, 

 9 and 10, are Eurasian to start with. 



6. Depressa and fnli'a are the most specialized away from 

 the primitive st-inifasciata penis of any of the Libellulas. (The 

 extreme specialization of Plathcinis and Ladonci suggests that 

 their stock may have been developed in Eurasia.) It is of com- 



