HYATT: GENEALOGY OF ACHATINELLHXE. 375 



ment of Ackatinellidce, and one would naturally expect to 

 find here a larger and if possible, higher development of the 

 family. But we are doomed to disappointment; the island 

 yields no arboreal species; the shells are all terrestrial 

 Hawaii is also favorable, for, as Baldiwn states: "Its ex- 

 tensive forests are as well adapted for the support of Achati- 

 nella as those of any of the other islands. ' Nevertheless, it 

 has a very small fauna. 



Niihau, lying to the southwest of Kauai, has an area of 

 90 square miles, and the highest peak is only 1500 feet, and 

 so far only one species of a sub-fossil shell has been found 

 there, Carelia sinclairi Ancey, which is extinct at the present 

 time. There are, however, certain correlations between the 

 topography and the distribution of these shells, already noted 

 by Baldwin (Hawaiian Almanac) which are of great interest, 

 for he states : ' ' That on a mountain chain with many culmin- 

 ating peaks the tendency is to a divergence of species ; while 

 on an individual mass of mountains concentrating towards 

 a single peak, the tendency is to a convergence of species.' 

 He also observes in treating of Molokai : * * It is about one- 

 third of the size (area) of Oahu, and like it has a mountain 

 range extending nearly thirty miles through its length. The 

 range is furrowed on both sides with deep valleys. Some 

 of these mountain gorges are very wide, and cut deep into 

 the narrow axis of the island. The larger ones have proved 

 an effectual barrier to the migrations of shells. The island 

 is thus divided into three natural sections, and each section 

 retains its own peculiar species without intermingling with 

 those of the next section. ' 



There is also a decided correlation between the relative 

 ages of the different islands, assuming that Kauai is the 

 oldest of those having living shells, and the kind of shells 

 that are found upon them; and also it seems obvious that 

 different genera came into existence in ascertainable succes- 

 sion upon different islands. 



This succession appears to accord, in all cases so far as 

 examined, with the genetic relations of these genera as de- 

 termined by a method which the writer has used successfully 



