110 ENTOMOLOGICAL NEWS [April, '22 



mon knowledge to distributionists that the Eurasian fauna and 

 flora are about one geological age in advance of the American. 



7. The Palaearctic species, because of their lack of near rela- 

 tives and because of their unrelatedness inter sc are the rem- 

 nants of a preglacial fauna, a fauna that was largely wiped out 

 when caught between the ice and the southern mountains. 



8. The holarctic 4-uiaciilata originated in Eurasia as it has 

 no near relatives in America. 



9. The genus as it exists in America today represents at 

 least three levels of development as are indicated by the hori- 

 zontal lines on Plate IV. 



10. The tropical Libellulas have probably entered the tropics 

 from the north or have been developed from northern stock, 

 also Ladona developed from the north to the south. 



11. Orthnnis with a penis that has broad lateral lobes may 

 be an American offshoot of the Libellulas with broad lateral 

 lobes. 



12. Libellula jcsscana gives us a Miocene date for its level 

 in the genus. 



From the foregoing it appears that the genus Libcllnla orig- 

 inated in a mild climate in premiocene times, but eventually 

 developed species into both the Transition and Subtropical 

 Zones ; that its dominance is past in Eurasia but is at its height 

 in North America. 



One point of general interest is that in a species or series of 

 species of Libelhda extending from north to south, the southern 

 individuals or species are small. Ris ( Libellulinen, Coll. Selys) 

 states that in julva and depressa examples from the southern 

 portions of their habitats are smaller. The same author states 

 that the Cuban aiiripcnnis is smaller than the American, that 

 the smallest examples of herculca come from Paraguay. How- 

 ever, in the last case the species is small in Mexico on the 

 northern border of its range. In Ladona the northern species, 

 jnlia, is largest, the southern species, dcplanata, smallest. 24 

 Dr. W. T. M. Forbes has pointed out to the writer that the 

 same is true in some North American Lepidoptera as they are 

 usually smallest on the southern edge of their range. Probably 



24 The reverse is true, according to Dr. Calvert, in Agrion macitlatum, 

 Gomphus dilatatus, etc. 



