296 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
GENERAL SUMMARY. 
It is now desirable to treat the present species in a somewhat comprehensive 
way, in order to bring out certain details in clearer relief and to set forth the wider 
significance of the detailed observations that have been described, as the author 
conceives their meaning. In concluding the sections concerned with the several 
primary varieties, summaries have been presented that render it unnecessary to 
recall the minor details or the subordinate matters of interpretation, of which the 
latter, save where they relate to classified concrete data, are always to be considered 
as secondary in importance to the observations themselves. It must not be for- 
gotten that the main purpose kept in mind throughout the study of this and of the 
other species has been to give a precise, detailed description of the primary and 
subordinate varieties and of their exact situations; the value of the task, so far as 
it has been accomplished, lies in the service it may be to future investigators who, 
after the lapse of years, may carry on similar studies in order to determine the 
nature and rapidity of the evolutionary changes that may take place in the interim. 
Nevertheless, the summarized observations reveal certain significant relations, and 
it is with such intrinsic meanings that we are now concerned. 
I. Partula otaheitana is ubiquitous in Tahiti, in one or another of its forms; 
it is usually abundant wherever the ecological conditions are such as to permit the 
existence of any Partula, and it is very variable. Therefore it offers an interesting 
contrast to all of the other species of its island, no two of which, indeed, are alike in 
the extent of the territory occupied or in the degree of their intrinsic differentiation. 
Partula hyalina is widespread but not abundant, and it exhibits very little diversi- 
fication among its colonies, now as heretofore. Partula clara has recently extended 
its range greatly, it has increased in numbers, and it has advanced in complexity, 
but as yet it has come to equal only a primary variety of otaheitana, such as affinis or 
sinistrorsa. Partula nodosa has paralleled clara in some of these respects, but falls 
short of the latter. Finally, Partula filosa is rigidly restricted to a single valley, 
where it thrives in numbers and varies considerably. Nothing could be more fav- 
orable for studies of the present kind than these conditions of the species of Tahiti, 
their diversity as regards matters of detail, such as the above, and the uniformity 
of the underlying principles of distribution and evolution. 
II. The closest relatives of Partula otaheitana, taken as a whole, do not occur in 
Tahiti; they are the many dextral species of Raiatea, and probably also the sinistral 
Partula mooreana of the neighboring island. These species occupy well-separated 
land-masses and well illustrate Jordan’s principle that related species are to be 
found in non-contiguous areas. Such a condition, however, is to be regarded as a 
derived one, for at the outset the strains that are destined to diverge in subsequent 
times are necessarily close associates in a geographical sense in correspondence 
with their genetic intimacy—which is amply proven by the descriptive account of 
the varieties in the present monograph. 
The occurrence of related forms in Tahiti, Raiatea, and Moorea means that in 
former remote times these islands were connected by land; that the common 
