386 HYATT: GENEALOGY OF ACHATINELLIDJE. 



occurs on other islands 'but has so far as I know no repre- 

 sentative on Oahu. They are, however, directly connected, 

 and barely separated as distinct species from other accom- 

 panying species that are placed by the same authors in the 

 genus Achatinella. They have identical young, the slender, 

 highly-polished, smooth shells and the colors of Achatinella,; 

 and no trace of the zigzag and marbled patterns and peculiar 

 colors common in Partulina. 



In general, it may be stated that the arboreal stations in 

 the Hawaiian Islands were occupied by highly colored shells 

 in which the coarse friable brown periostracum of the ground 

 shells is absent and the color patterns were highly complex. 



The differences evolved in these distinct genera are thus 

 correlated with their different stations and distribution, and 

 they certainly appear to have arisen in connection with their 

 change of environment. 



It seems obvious also that these could not have been evolved 

 had not the new fields and stations been open and unoccu- 

 pied. If we assume that the observed differences were ac- 

 quired in consequence of the migrations of the ancestral 

 forms of each group or species into new situations, the whole 

 complex association becomes apparently explicable. 



It is also obvious in these islands that the variations are 

 not only coincident with migration into new fields and sta- 

 tions, but they are also limited to these geographically, and 

 species are not as a rule maintained in their original form 

 when new migrations take place. 



Species are, however, traceable by hybrids or by grada- 

 tions into others along lines of unbroken continuity through- 

 out the eastern chain of Oahu in Bulimella, Achatinclla, and 

 Apex wherein they can be followed along the same lines of 

 migration to their termination in the western range. Fin- 

 ally, the same may be done in all the groups that range 

 from island to island, the connections of course being less 

 perfect than in forms living upon one and the same island. 

 The species, however, can be followed by groups and some- 

 times by graded variations so slight that particular forms can 

 be pointed out as the migrants that must have come from one 



