RESUME. 309 
the identical external influences of that area; the sinistrality of /gva is not invariable 
in Maruapoo Valley; the characteristic smaller size of exigua is not paralleled by a 
depauperate condition in any of the accompanying species, P. hyalina, P. clara, 
and P. otaheitana—the last of which is uniformly sinistral and not dextral. It 
would seem, then, that the hereditary qualities of the earlier inhabitants or of the 
first immigrants are the real determining causes of the characters of their descend- 
ants, which might vary subsequently, but in no discernible way on account of 
qualitative effects of the environment. 
CHAPTER VII. 
By far the greater part of the Partula population of ‘Tahiti consists of repre- 
sentatives of the complex series P. otaheitana, which exists in few or several of its 
manifold forms in every valley where any larger snails whatsoever were secured. 
More than 20,000 adults, 6,000 adolescents, together with many thousands of 
advanced embryonic young, constitute a wealth of material which is peculiarly 
favorable for an exhaustive analysis; for not only does the species occur in con- 
siderable numbers in practically every habitable area of the island, but it is also 
differentiated with extraordinary clearness into primary, secondary, and even 
tertiary varieties. Hence the condition of one of its major sections may exceed in 
complexity that of an entire contrasted species, like P. clara or P. nodosa. In view 
of these facts, it is manifestly impossible to give at this juncture more than an out- 
line of the condition of this species and of its evolutionary history. 
Taken collectively, the shells of otaheitana appear in both modes of coil, with 
colors ranging from light yellowish-white to deep seal-brown; they vary in the 
measurable characters of size and shape in ways that may be statistically defined. 
The pro-otaheitana stock was a derivative of a widespread series which became 
isolated when Tahiti was separated from the other elements of the Society Group, 
but for the purposes of the present study the extrinsic relations of the species are 
not important. 
Subsequently, the original stock became differentiated into eight primary 
varieties; otaheitana sensu strictu, amabilis, rubescens, affinis, the sinistrorsa-sinis- 
tralis-crassa group, and lignaria. ‘The first of these now exists in Fautaua Valley 
as the most generalized and most primitive section of the species; its colonial com- 
plex of characters comprises virtually all of those which are exhibited by the other 
more specialized primary varieties, inasmuch as it includes sinistral and direct 
shells of varying colors and sizes and with banded as well as unbanded patterns. 
The next division, amabilis, inhabits a contiguous section to the north; its repre- 
sentatives differ in successive valleys, but always without relation to geographical 
or other external circumstances. Eastward and southward of the area occupied 
by amabilis is the territory of two absolutely independent varieties, rubescens and 
affinis, which have almost identical geographical limits, yet they stand in the 
sharpest possible contrast to one another; rubescens is large, always sinistral, and 
yellow or reddish in color; affinis is predominantly dextral, small in size, and stout 
in form. ‘They do not interbreed, so far as the evidence goes, even though they 
must be regarded as derivates of the same pro-otaheitana stock. 
