228 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
THE COLONIES OF TAHITI NUI—APIRIMAUE TO TAHARUA VALLEYS. 
Passing westward from the last Taiarapu colony, we must return to the major 
land-mass of Tahiti. It has been stated earlier that Haoma Valley in the peninsula 
is not inhabited by sznistrorsa, as far as the collection may be taken to represent the 
actual population; if it occurs at all, its numbers must be very few. Likewise Oopu 
Valley, which is the easternmost valley of the southern tier in Tahiti nui, seems to 
have no sinistrorsa inhabitants, although rubescens flourishes here as nowhere else 
in the island. The total range of sinistrorsa is thus interrupted by a lacuna extend- 
ing from Vaipoe to Apirimaue. 
The region from Apirimaue westward is a subsidiary area which comprises 
the original range of the primary variety, as Garrett has stated in the most explicit 
terms. From this, sinistrorsa has passed to occupy the four valleys of Taiarapu, 
and from it also emigrants seem to have passed in small numbers to the eastern 
quadrant; a single immature snail found in Faone Valley is the positive observation 
upon which this statement is based. 
The colonies of this area are extremely complex and they are much differentiated 
inter se. Whether or not their diversity is recent in origin, the fact remains that for 
the time of investigation sinistrorsa does not “present the same features through 
all the valleys for a distance of 10 or 12 miles.” Nor is it by any means always 
sinistral; dextral members actually outnumber the typical reversed snails in at 
least one valley, while at other points sporadic or abundant dextral mutants make 
their appearance. Dimensional differences that must have escaped the notice of 
Garrett are brought to light by the statistical treatment of the measurements of the 
shells. Such being the case, it is possible to conduct a profitable analysis of the 
sintstrorsa material from this region, always with a view to the general problem 
as to the relative values of congenital and environmental factors of racial differ- 
entiation. 
APIRIMAUE VALLEY. 
The members of this association are all sinistral, and fall into the three color- 
classes distinguished in Vaiaaia. ‘The type apex is represented by 16 snails (5.6 per 
cent), phea by only 4 (1.4 per cent), while 264 distinctly banded cestata make up the 
bulk of the colony. It was here, the last valley of the range of affinis, that Garrett 
stated he “took a few examples of sinistrorsa’’; now this primary variety exists in 
abundance. 
In statistical respects (table 171) the phea class departs greatly from the cestata 
class in absolute measures, being smaller in all cases. On casual acquaintance, the 
observer might suppose that they were sinistral relatives of the few dextral affinis 
that exist here, on account of the similarity in coloring; but their form is character- 
istic, while furthermore the offspring of the afinis are always dextral. Other con- 
siderations are adduced below, enforcing the conclusion that the so-called phea 
snails are true constituents of the simzstrorsa association, in this valley as in Vaiaaia 
and elsewhere. The other details of the statistical table need no verbal explanation. 
All shells are toothless, as in Taiarapu. 
