250 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
PARTULA OTAHEITANA SINISTRALIS Pease. 
GENERAL CONSIDERATIONS. 
Passing westward from Taharua, the last valley occupied by Partula otaheitana 
sinistrorsa proper, we enter the territory of the second group belonging to the triple 
series now under consideration; this area comprises the larger and smaller valleys 
from Teohu to Vaipuaru, inclusive. The distinctive peculiarities of the colonies were 
regarded by Pease as of specific value, and he named the kind Partula sinistralis. 
Garrett’s description is their only characterization in the original literature, but Gar- 
rett differed from Pease in that he related sinzstralis to sinistrorsa, and indeed, by 
implication, he subordinated the former to the position of a section of the latter. In 
the present study sinzstralis is treated as the second division of the tripartite “sinis- 
tral series of the south and west,’ whose other members are sinistrorsa and crassa; it 
is intimately related to both of these and is transitional from the first to the second, 
in correspondence with the location of its SoTENATOLY between the areas occupied by 
sinistrorsa and crassa. 
In Garrett’s paragraph relating to sznistralis, which has already been given 
(p. 220) without comment, the points of departure from the sinistrorsa type are 
specified sufficiently in a qualitative way; to these the following detailed analysis 
will add quantitative differentia. ‘The alliance of the two groups is manifested by 
the predominating reversal of the coil in sinzstralis, by the absence of ground-colors 
like those of rubescens, by the occurrence of banded forms of marking referable to 
the cestata type among sinistrorsa, and by the existence of the color-forms called 
apex and phea in certain of the eastward colonies. Other characteristic color-forms 
make their appearance, which are suggestive of the distinctive crassa types found 
in the western sector of Tahiti nui. 
It will appear that sinistralis is not always stunted and dentated, as Garrett 
states, nor is it always sinistral; some of the most western colonies comprise numer- 
ous dextral individuals, so that in general composition they come to resemble 
certain eastern sinistrorsa associations. Furthermore, we find sinzistralis in two 
large valleys, as Garrett says, but it exists in many lesser topographical elements as 
well, and even in the coastward forests outside the mouths of the valleys. Undoubt- 
edly Garrett knew that the snails were not confined to the two major valleys 
situated between Taharua and the southwestern corner of the island, but presum- 
ably he ignored the lesser areas and regarded the larger elements as inclusive of 
the rest. 
The line of division between the range of sinistralis and that of sinistrorsa 
passes between Taharua and Teohu Valleys, as stated; but there is no topographical 
feature at that point to account for the abrupt transition from the one kind to the 
other. On the contrary, one might almost view the valley areas of Taharua and 
Teohu as continuous, because much forest grows along the coastal face of the 
buttress between the two clefts, wherein snails are to be found, though in very small 
numbers. At its western end the sinzstralis territory extends beyond a well-marked 
ridge that runs down to the coast at the southwestern corner, so as to include one 
valley of the western sector, viz, Vaipuarii. 
