XV] ZOO-GEOGRAPHICAL DISTRIBUTION 287 



and, apart from the Macromiini, the Oriental region shares with 

 the Neotropical this paucity of forms. The Platycneminae, 

 however, are essentially a tropical group. It is peculiar that the 

 Oriental and Neotropical agree in possessing rich developments 

 of Megapodagrioninae and Protoneurinae, but differ in that the 

 former alone has a rich development of Platycneminae. 



I am inclined to associate the absence of Pla'ycneminae in 

 Neotropica with the presence of the unique Pseudostigmatinae. 

 These latter will, I believe, eventually be shewn to be the lost 

 Plaiycnemine stock of the Neotropical Region, which has reached 

 its present form through a hypertrophy of wings and abdomen, 

 brought about in correlation with the adoption of the extraordinary 

 habit of breeding in the epiphytic Bromeliads of the dense tropical 

 forests. 



The Nearctic Region. 



In this region we include the whole of the North American 

 Continent, together with the temperate parts of Mexico. The 

 region is not nearly so well differentiated, as regards its Odonata, 

 as the Neotropical. Out of 59 genera known to occur, only 24, 

 or 41 per cent., are peculiar or entogenic 1 . The chief reasons for 

 this are (i) the presence of a fairly abundant Holarctic fauna 

 consisting of genera shared in common with Palaearctica, (ii) a 

 considerable southern incursion of ectogenic genera from Neo- 

 tropica, together with other genera which may be regarded as 

 dientogenic for both Nearctica and Neotropica. 



The most striking point about the Nearctic fauna is the rich 

 development of the tribes Gomphini and Eucorduliini. The 

 seven genera of the latter tribe confined to Nearctica probably 

 represent the highest expression of the ideal Odonate-type yet 

 reached by the Order, and can only be paralleled by the Australian 

 Hemicordulia-group. 



The Nearctic region is as poor in Zygoptera as the Neotropic 

 is rich. Only 15 genera, belonging to three subfamilies, occur; 

 and of these, only two are peculiar. But for the presence of 

 Hetaerina (fig. 151) and Argia, which seem undoubtedly to have 

 come originally from Neotropica, there would be left only a 



1 See foot-note on p. 286. 



