xlii NOTES ON ZOOGEOGRAPHY. 



one specimen from Kauai (L. fossilis, Vol. XXI, p. 61), is no;v 

 known from many beds on the north, west and south shores 

 of Oahu, from Molokai, Maui, Kahoolawe and Hawaii. This 

 group of very closely related forms, now extinct, was commo'i 

 to at least six of the islands in the Pleistocene. One species, 

 L. subcylindracea, was common to Oahu, Molokai and 

 Kahoolawe, and the forms of Maui and Hawaii are barely 

 distinguishable. The extinct forms of the L. oryza group 

 from Oahu to Hawaii are so very similar that we have doubts 

 of their specific distinction. 



Upon the hypothesis that the snails had been distributed 

 by ocean drift, birds, etc., it would be expected that the num- 

 ber of species common to two or more islands would be in- 

 creasing by the occasional action of such agencies. The fact 

 is, that species common to two islands were more numerous 

 in the Pleistocene than they are today, even though the ex- 

 ploitation of the fossil deposits has only begun, and the recent 

 fauna has been studied for years. Such a condition is 

 exactly what we would expect if the islands had been united 

 in the late Tertiary, and their common faunal elements had 

 been distributed by known and normal modes. 



The hypothesis that Achatinellidce (or rather Amastridce) 

 first come to Kauai, and thence to the other islands, as advo- 

 cated by Professor Hyatt (p. 371 et seq.) no doubt had its 

 inception in the orthodox view of the relative geologic age of 

 the islands. The biological evidence relied upon by Hyatt 

 has proved, now that the fauna is more fully known, to 

 indicate no such succession of faunas. Taking the fossil 

 species now known into the account, it becomes obvious that 

 all the islands have, or in the Pleistocene had, very closely 

 related faunas of the primitive groups: Leptachatina (cer- 

 tainly the most primitive genus of the family), Amastrella, 

 Cyclamastra. Between these closely related species it would 

 be absurd to claim that those of Kauai are more primitive 

 than those of Hawaii, or any other island. The same evolu- 

 tionary stage is equally represented by species on all the 

 islands. Hence, it seems likely that these common faunal 

 elements remain from a former time when the islands were 



