66 



INSECTS OF SAMOA. 



the apodemic species, or 106 species altogether. This is an abnormal ratio, 

 being an average of barely two species to the genus, but the proportion of species 

 to genera will probably be materially increased by further collecting, though 

 it is necessarily always low when the total fauna is small. Of these fifty-four 

 genera only eight, belonging to six distinct families, are endemic, and these are 

 all monotypic ; therefore, isolated as the group is, it cannot in a biological sense 

 have been isolated very long. If we compare Hawaii, with a very prolonged 

 history of permanent isolation, we shall find that most of the principal genera, 

 rich in species, are endemic, and some of these so peculiar that they have no 

 near relatives elsewhere ; the endemic genus Hyposmocoma contains 190 species. 



Taking the remaining forty- two genera in order of magnitude, we find : 



Labdia, seventeen species, all endemic but two ; a considerable Indo- 

 Malayan genus, also freely colonising Australia ; the larvae are refuse-feeders, 

 and the islands are apparently well suited to them, the genus being equally 

 prominent in Fiji and the New Hebrides. 



Decadarchis, nine species, of which seven are endemic ; this genus, of 

 which the larvae also feed on refuse and dead wood, is probably Indian by 

 origin, like the last, occurring also in the African and Malayan regions and in 

 Australia, but apparently attaining its greatest development in the South 

 Pacific islands. This and the preceding genus have the obvious advantage of 

 being able to find suitable larval food in any island that they can reach ; they 

 alone show considerable specific development, probably due to this suitability 

 rather than to any special earliness of colonisation. 



Hiero?nantis, five species, of which two occur also in Fiji ; a small Indo- 

 Australian genus, probably also a rabbish-feeder. 



Acrocercojjs, five species, two of these imported ; a very large cosmopolitan 

 (but especially Indian) genus ; the larvae mine in leaves, usually of trees and 

 shrubs. 



Thiotricha, five species ; a considerable Indo-Australian genus, larvae 

 case-feeders on leaves of plants. 



Eucosma, four species, one of these introduced ; this very large genus is 

 cosmopolitan, but especially characteristic of the Northern hemisphere, not 

 much developed in the Indo-Malayan region, and very little in Australia and 

 New Zealand. 



Stathmopoda, three species : a large genus, mainly Indo-Australian, the 

 larvae mostly rubbish-feeders. 



