34 FAUNA HAWAIIENSIS 



to which are true species is as yet by no means absolutely settled. In the females the 

 climax of difficulty is reached, for these have no structures suitable for distinguishing the 

 species that can compare with the terminal appendages of the abdomen of the ^, while 

 the superficial distinctions, such as colour, details of nervuration, etc. are notably variable. 

 All the species of Agrioit are peculiar to the islands and are probably all related to one 

 another, as more or less transitional forms are found between the different groups, and 

 it is probable that all originated from some single species which reached the islands in 

 remote times. Of the other four dragon-flies the Tramea, Pantala, and Anax jimius, 

 are no doubt natural immigrants, being all species of powerful flight and all are distri- 

 buted throughout the group, whereas a large proportion of the species of Agrion are 

 either restricted in range to one island, or when occurring on more than one are tending 

 to form other distinct species, or local forms. The larger Anax, which is a very fine 

 insect, is so far as is known peculiar to the islands, and has probably been established there 

 sufficiently long to acquire characters which separate it from any other of the genus. 

 It is very powerful on the wing, and is widely distributed over the islands, and extends 

 its range far up the mountain sides. Another moderate-sized species, assigned to 

 Sympetrum by Karsch, but for which Kirby has established a genus, Nesogonia, is also, 

 so far as is known, peculiar to the islands. It is generally distributed over the group, 

 in the mountains, and is notably variable in size, colour and nervuration. 



If we limit our investigation to the species of Agrion it will be seen that in the 

 number of species peculiar to it, Kauai ranks easily first of the six larger islands. 

 Excluding A. xanthome las and A. pacificum, species ubiquitous over the islands, seven 

 species are restricted to Kauai, nor has it any species that even extends to the neigh- 

 bouring island of Oahu. The latter island has four species peculiar to itself, and five 

 others which are found also on one or more of the others. Maui, Molokai and Hawaii 

 have each but a single species peculiar to them, while the little island of Lanai with 

 seven or eight species has none. It should be added however with regard to these 

 islands that some of the species upon them form varieties very distinct from the typical 

 examples, and this is especially the case with several of the species found on Hawaii, 

 where diminution in size and corresponding changes in nervuration are often evident. 

 Nevertheless the occurrence of examples in a condition intermediate between the typical 

 and extreme forms of such species renders it inadvisable to consider them as belonging 

 to more than one species. The following table shows the percentage of species of 

 Agrion peculiar to each of the islands. 



Species peculiar to. Total number of species. Percentage. 



9 777 



lO 40 



8 12-5 



7 — 



10 10 



9 ii'i 



J 



