Xliv NOTES ON ZOOGEOGRAPHY. 



Amastrida could have been ancestral to the Achatinellida . 

 The points of agreement between Kauaia and Achatinella 

 phaozona, noted by Hyatt (pp. 398-9), pertain to shell char- 

 acters of little or no phylogenetie significance, and leave the 

 important anatomical differences absolutely untouched. In 

 fact I have failed to find any characters in A. phccozona which 

 indicate it as an ancestor even of the species immediately 

 related far less of the whole Oahuan genus Achatinella ! 



The absence of arboreal Achatinellidce from Kauai has 

 provoked comment because the forests seem well adapted to 

 tree shells. It is a grave difficulty from any point of view. 

 I am informed that Achatinella, introduced there thrives. ( 

 Several hypotheses may be formulated. (1) It is possible 

 that the Achatinellidce reached the region later than Amas- 

 tridce, and after Kauai had been isolated from the remainder. 

 This seems the simplest explanation. (2) Achatinellidce 

 may have existed on Kauai, but becom/ extinct from some 

 unknown cause, as the horse family in America became ex- 

 tinct. Or (3), it is possible that the events attending the 

 submergence of the old Hawaiian land did not allow tree 

 snails an opportunity to gain access to the new forests on the 

 Kauaian volcanos. However this may be, speculation upon 

 a negative character of this kind seems rather unprofitable 

 employment in the present condition of our knowledge. 



In my opinion there is no evidence whatever indicating 

 southeastern Oahu as the point of divergence of the snails 

 of that island. The geological features and the distribution 

 of species are both too "mature" to indicate one place more 

 than another in the Main Range as the initial point. In 

 Hawaii both the geological structure and the distribution of 

 Achatinellidce point to the Kohala mountains as the area from 

 which land snails have radiated. Species and varieties pro- 

 gressively diminish from this region down the east and west 

 coasts. 



From studies on Amastrida (Vol. XXI) I concluded that 

 the Waianae fauna had been independent of that of Koolau 

 from the early period when all the islands were connected 

 until late Pliocene or more likely Pleistocene. The tree shells 



