384 HYATT: GENEALOGY OF ACHATINELLID^E. 



tooth, there is a decided tendency towards the evolution of 

 an additional spiral fold on the columella. 



The topography of Oahu changes as one proceeds north- 

 wards. The highest peak in the eastern range is Mt. Kona- 

 huanui, 3105 feet, situated about 15 miles from the southern- 

 most point of the island. From this peak to the northern 

 end of the island there is a gradual lowering of the heights 

 until 'beyond Waikane valley, the <crest is only about 2360 

 feet high and the intermediate valleys are separated by 

 wooded spurs that do not oppose any serious obstacles to the 

 migrations of the species. It is obvious that this relatively 

 flat, low-lying region must have quite different conditions 

 from the much more broken southern part near Honolulu. 



The crest of the eastern range shuts off from the interior, 

 the trade winds that blow strongly from the northeast for 

 nine months in the year. The crest therefore gives much 

 greater shelter to the inner or western sides of the hills. 

 These winds also beat upon the unsheltered eastern side of 

 the Konahuanui range and here the difference on this ac- 

 count alone is apparent in the difference in the vegetation 

 of the two sides; the eastern sides being scantily and the 

 western thickly covered with trees. 



The Bulimellas of Oahu thrive high up on the ranges and 

 extend to the outer, wind-beaten, eastern or coast side of the 

 eastern range of the island between Waiahole and Hauula val- 

 leys. The Achatinellas, on the other hand, affect more shel- 

 tered locations, are unfavorably affected by this wind-beaten 

 side and the species become smaller and individuals less nu- 

 merous as one proceeds northward along the eastern side of 

 Oahu toward the northern parts of the island. Achatinella 

 was not very successful in crossing the middle parts of the 

 island to the western range, and not a single Bulimella suc- 

 ceeded in crossing the central plain of the island. 



Apex, however, thrives in locations between Achatinella 

 and Bulimella, und while it was less successful than Achati- 

 nella in crossing the crest of the Konahuanui range to the 

 coast side, it was on the other hand, the group best suited to 



