PARTULINA, SECTION BALDWINIA. 99 



those which distinguish this series. The number of forms_ 

 might be multiplied almost indefinitely, but the above will 

 suffice to indicate the general character of the variations ex- 

 isting within this single colony. 



" As in the case of P. horneri, a distinct tendency is ob- 

 servable, though by no means so marked, to the segregation of 

 the different color varieties upon individual trees, indicating 

 that isolation has been sufficient to permit differentiation 

 within certain limits, while the fact that many trees support 

 a sprinkling of other varities, added to the completeness of 

 the intergradation, proves that intercommunication has been 

 to some extent potent in limiting the amount of the diver- 

 gence. 



* The following facts bear upon the question of intercom- 

 munication between the several parts of the colony. The pua 

 and mamani trees, upon which the shells live, rarely touch 

 each other, and are usually separated by a distance varying 

 from a few feet to a hundred yards. The land is pasture 

 and the grass under many of the trees not in the open is 

 deep. There is thus no chance for the shells to pass freely 

 from tree to tree. 



" Upon Oahu and the other islands of the group deep 

 valleys and high ridges in most localities tend to the more or 

 less complete isolation of shell colonies, and also present 

 diverse conditions of foliage and environment favorable to 

 the differentiation of new forms. The environment of the 

 present colony on the contrary is exceedingly uniform and 

 hence presumably unfavorable to the origin of new varieties, 

 but the isolation of the trees and the open nature of the 

 ground form barriers to free intercourse quite as effective 

 as ridges and valleys, and hence tend to the perpetuation of 

 any chance varieties that may arise. 



" The author is aware that some observers consider the 

 Achatinellidce to be active and rather extensive travelers, but 

 his study of the three species under consideration points to 

 the opposite conclusion. The fact, as noted above, that logs 

 and rocks under the trees form the permanent abode of such 

 shells as chance to fall from above, seems to show that the 



