AMASTRA, OAHU. 157 



groups of Achatinellse in the Main or Koolau range. Fol- 

 lowing this long period of isolation, in quite modern times, 

 within the lifetime of existing species, the two radiation- 

 centers were transiently connected by a forest area across the 

 intervening saddle, which had meantime been built up from 

 a lower level or from below sea-level. This allowed the migra- 

 tion of a few virile species from range to range. 



Aside from this geologically very recent exchange of species 

 between the two Oahuaii radiation-centers, there is no evi- 

 dence whatever to show that the fauna of either range was 

 derived from the other. The truth probably is that both 

 arose from an early tertiary fauna which occupied a more 

 extensive land, upon which the existing volcanic deposits were 

 superposed during Neocene time, with synchronous subsidence 

 of the ancient ridge. I cannot find one shred of evidence for 

 Hyatt's contention that the southeastern end of the Main 

 Range was the primary radiation-center and that the Waianae 

 fauna was derived from the eastern range. 



The deposits containing fossil land shells are probably 

 Pleistocene, possibly Pliocene. That on Diamond Head is be- 

 lieved by Branner to have been an old forest deposit covered 

 with talus. Its fossils belong to modern groups of the same 

 district, though not now living in the same locality. 



The first Achatinella known, Helix apex-fulva Dixon, was 

 obtained in Oahu (June, 1786) from a necklace prob- 

 ably made in Kawailoa. valley. In 1819 the French corvette 

 Uranie visited Hawaii, Maui and Oahu, lying in Honolulu 

 harbor. In the neighboring valleys, probably Nuuanu and 

 Manoa or Palolo, the following species were obtained : Achat- 

 inella vulpina, gravida var. gracilis, decora, lorata; Amastra 

 turritella, textilis, tristis ; and Lept. ventulus. Amastra lute- 

 ola also may have been from Oahu, but it is more likely a 

 Hawaiian shell related to A. flavescens. Amastra spinzona 

 they also obtained, no doubt from the natives, as it occurs 

 only in western Oahu. The next collection of importance was 

 made by Lord Byron in H. M. S. Blonde, 1824, who brought 

 home a shell necklace, composed of Achatinellida special to 

 Kawailoa valley, near the western end of the main range, and 



