PARTULA OTAHEITANA. 185 
individuals. Yet the latter represent so many valley types, and it is interesting to 
ascertain what the general condition of the variety is, when defined on the basis of 
such valley types taken as genetic entities, aside from the numerical abundance of 
their representatives. 
PARTULA OTAHEITANA AFFINIS Pease. 
GENERAL CONSIDERATIONS. 
Hitherto in dealing with the primary subdivisions of the present species we have 
followed a regular geographical order, beginning with P. otaheitana otaheitana of 
Fautaua Valley, which merges into P. 0. amabilis of a short northern series of 
valleys; immediately beyond the latter’s range P. 0. rubescens appears, and extends 
widely around Tahiti nui and Taiarapu without varying sufficiently in major charac- 
teristics to justify the establishment of secondary varieties with distinctive names. 
We must now return to the northern sector of Tahiti nui, for the primary subdivision 
affinis, now to be taken up, begins its range just beyond the territory of amabilis, 
and accompanies rubescens in nearly all of the valleys of the eastern sector and of 
Taiarapu. 
The variety afinis presents new features of distribution and intrinsic variation, 
as well as many that have been encountered in the study of the earlier-described 
divisions. It is greatly diversified as compared with rubescens, although all of 
its variants agree in the distinguishing characters of the primary variety, which 
features are traceable to those of the common ancestral stock of the whole species, 
now best represented by P. o. otaheitana. The subdivision as a whole is so clearly 
demarcated that it was described by Pease as an independent species, Partula 
affinis; furthermore, one of its subordinate color-forms has been given the status of 
a major variety, viz, dubia. But a closer study of the snails and of their inter- 
relationships leads inevitably to the conclusion that affinis is a variety of P. otahe1- 
tana, although its internal differentiation equals that of such a distinct species as 
Partula clara. 
The range of P. o. affints, taken as a whole, includes the entire area inhabited by 
rubescens—its very antithesis in most respects—while it also comprises valleys in 
Taiarapu which lack rubescens, but which bear members of still another primary 
variety, sinistrorsa. Specifically, affinis spreads from Tuauru Valley throughout 
the eastern sector and throughout Taiarapu; its range ceases in Tahiti nui with the 
same valleys—Oopu and Apirimaue—that constitute the limits of the habitat of 
rubescens. tis noteworthy that these two sharply contrasted primary types occupy 
in common so many valleys situated in different parts of the whole island. The 
essential point, which becomes increasingly clear, is that one and the same environ- 
mental situation could scarcely produce two antithetic types in and by itself. 
The original description of Partula affinis by Pease (Amer. Jour. Conch., 1867) 
is as follows: 
“Slightly elongately ovate, rather solid, compressly umbilicate, dextral,' finely, 
roughly, and irregularly striated longitudinally, transversely very minutely striate, sutures 
1In the Latin description, also, ‘“‘Anfr. 5, plano-convexis, ultimus ? longitudinis teste subeequans.”’ 
