HYATT: GENEALOGY OF ACHATINELLHXE. 385 



cross the central plain of the island and occupy the western, 

 or Waianae range where it is by far the most abundant shell.* 



Bulimella has a rougher shell and more uniform coloration 

 in the southern parts of the range, but changes as it proceeds 

 northwards and especially on crossing the crest in the north- 

 ern part of the range. The species evolved in this region 

 are more numerous, larger, the shells smoother and more 

 brilliant in color and more elaborate in their patterns. 



Achatinella throws, or rather did in Gulick's time (1853- 

 54) out a colony of species that crossed the crest to the coast 

 side, and the changes that occurred in this colony were very 

 significant. They consisted of comparatively small, bright- 

 colored, banded species which resemble those that occur to the 

 north and on the same side of the mountain range, but are 

 widely separated from them by a barren region having no 

 shells of any kind. The main body of Achatinellas marched 

 northward on the inner watershed of the eastern range of 

 Oahu, here and there evolving large, brilliant shells until they 

 reached the northern region of the island. There the shells 

 are smaller, and although still striped, are sensibly distinct 

 from their southern progenitors. These small shells sent mi- 

 grants across the range to the coast side, the same species 

 sometimes occurring on both sides of the range. The num- 

 ber of species of Achatinella in this region also sensibly 

 diminished, where as in Bulimella the number of species in- 

 creased. 



The small northern species are so distinct that although 

 closely connected by gradations with the southern forms, a 

 limited number of them have been set apart by several au- 

 thors as a distinct genus named Eburnella by Pease I have, 

 however, not been able to separate any of them from their 

 southern affines. Some authors have also thought that cer- 

 tain of these small shells belonged to a genus Partulina that 



* in 1898 Professor Hyatt published a short paper in ' ' Science ' ', 

 volume 8, p. 395, in which he concludes that the genera Bulimella, Acha- 

 tinella, and Apex of Oahu originated from a common ancestor, the 

 Achatinella phceozona of Kuliouou valley near the southern end of the 

 Konahuanui range of mountains. 



