82 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
In the collections of the present research, filosa is represented by 211 adults of 
various colors, about 40 adolescent snails, and more than 60 embryonic young and 
eggs taken from the gravid full-grown individuals. In each of the four years of 
field-work, material was obtained from Pirai. On account of the havoc wrought 
by the cyclone of 1906, it was possible to penetrate only a short distance into the 
valley in that year, when 52 jilosa out of 371 adults were secured (14 per cent). In 
1907 a total series of 295 adult Partule was obtained from the intermediate valley, 
of which only 24 (8.13 per cent) were filosa. The following year a small collection 
was made again from the middle portion of the inhabited area, in which this species 
amounted to 11.2 per cent. Finally in 1909 a journey was made to very near the 
limit of occupation toward the higher part of the valley; at that time, 123 adult 
filosa were obtained and these constituted 25.1 per cent of the series that was 
preserved. But 400 to 500 other snails representing P. otaheitana were also taken, 
to be immediately returned to their environment; hence the frequency of filosa 
is really about half of the indicated percentage for the year. It is clear that this 
species 1s not restricted to the lower part of Pirai Valley, although it is true that 
it exists in relatively greater numbers in the lower levels. It appears also that 
statistical differences are brought to light when the collections of different portions 
of the inhabited regions are analyzed in detail, as described beyond. 
The single valley inhabited by fi/osa lies on the northwestern side of Tahiti 
nul, almost at the exact center of the leeward slopes of the whole mountain mass 
(cf. plates 5a,9,10,and 11). Inthe sector which is bounded by Fautaua Valley on the 
west and Papenoo Valley on the east, the land rises to the highest peaks of the island, 
Mounts Orohena and Aorai. The seaward side of this sector is deeply cut by Pirai 
to the west of Point Venus and by Ahonu and Tuauru Valleys to the east of this cape, 
all of which are of the second order of size. Other valleys and gullies of lesser depth 
and extent also occur here, but on the whole this sector forms a relatively compact 
triangular land-mass. ‘The depression of Pirai Valley itself is gradually lost in the 
heights, so that it does not communicate with either Fautaua or Papenoo. 
The flat plain of the coastal shelf runs well up into the valley, where wide cane 
fields and coconut groves occupy the level or nearly level floor. Along the lower 
slopes of the bordering ridges and along the stream there are dense thickets of hibis- 
cus and guava trees. About 1.5 miles from the coast the valley narrows suddenly, 
the sides become more precipitous, and the succulent vegetation of the shaded and 
moist interior regions is met with. 
The first snails were found a little more than 2 miles inland, at an altitude of 
375 feet, on the plantain (fei), Dracena (ti), ginger (opul), turmeric, and birds-nest 
fern (oaha). A few were obtained from wild pineapples and Pandanus. 
In 1909 I found extensive changes in this part of the valley, owing to the devel- 
opment of vanilla plantations, as the result of which the undergrowth had been much 
reduced, so that the whole lower region was rendered practically uninhabitable for 
Partule. 
Higher up, the plantains become more numerous, and thick growths of the 
caladium (ape) occur, especially in the steep pocket-like ravines along the walls of 
