CHAPTER I. 
THE GENERAL FEATURES OF THE POLYNESIAN REALM IN RELATION TO 
THE DISTRIBUTION OF THE SPECIES OF PARTULA. 
OUTLINE OF THE SITUATION. 
The present investigation is concerned with the characteristics displayed by 
certain Polynesian species of Partula and by their varieties, taking into account the 
environmental situations of all distinguishable forms. It is necessary, therefore, 
to consider the geography, geology, and climatology of the inhabited areas, as well 
as to make an analysis of the biological conditions that obtain in Polynesia. This 
descriptive review refers primarily to the southeastern portion of the whole region 
inhabited by the genus, where Tahiti and the rest of the Society Group are situated, 
because these islands are characteristic representatives of those that are to be 
found in Oceania, and because the writer’s field studies have been conducted there 
more intensively than elsewhere. In addition, it appears that nearly one-half of 
all of the species are found in the Society Islands only, while, furthermore, these 
species belong, for the most part, to the most typical subgenus of the series, accord- 
ing to Pilsbry and others. 
As a basis for the following description, it may be established at the outset 
that representatives of the genus Partula are found only on oceanic islands spread 
throughout a vast area of the south and west Pacific Ocean. They do not exist in 
the Hawaiian Group—the home of the related Achatinellida—although to the west 
they reach as high a latitude in the northern hemisphere. In the wide region of 
their occurrence they are distributed locally; that is, the genus is not represented 
in all groups of islands, nor do the species present in a group occur in all of its 
island elements. In general, it may be said that Partule are absent from the 
“low” islands, or coral atolls, and from most of the small “high”’ islands of volcanic 
and other nature; certain records attributing species to the Tuamotu and other 
atolls are undoubtedly erroneous. In a few instances, an island formed by the 
emergence of a coral mass above the sea may be inhabited by Partulz, as in the 
Cook and Austral Groups. 
The situation being what it is, it would be impossible to find a more ideal 
combination of circumstances for the investigation of the members constituting a 
definite biological group, and of their geographical distribution. ‘The total area of 
occurrence is large, exceeding that of the United States; within this, the habitable 
bodies of land are separate islands, more or less distant from one another, associated 
in lesser or greater numbers in groups that lie relatively near or far apart. Hence 
the degrees of geographical relationship are marked with extraordinary distinct- 
ness, without any question of intermediate connections that intervene between 
comparable ecological regions of a single continent. Furthermore, it has long 
been known that within the confines of a solitary island the areas suitable for the 
13 
