PARTULA HYALINA. 4I 
lack this species, while it is more than probable that on account of the island-wide 
distribution of the species he assumed the existence of Ayalina in some of the larger 
valleys from which it now appears to be absent. Mayer is the only other author who 
has dealt with the distribution of this species, and he found it in all of the six valleys 
from which his collections were taken, namely, Pirai, Hamuta, Fautaua, Tipaerui, 
Maruapoo, and Vaihiria. 
The general census (table 9) gives the exact numbers of hyalina taken in the 
several valleys, as well as their relative frequency, namely, their percentage value of 
the whole population. ‘These figures relating to adult snails give as accurate a 
determination as possible of the relative abundance of hyalina, for there was no 
discrimination exercised in the collection of snails, except in two cases. The first 
exception is in the case of Pirai Valley, where in 1909 particular attention was paid 
to Partula filosa; on this occasion several hundred individuals of otaheitana were 
obtained and counted and were at once returned to their forest habitat. Another 
exception must be made in the case of Faarahi, to which a second visit was made 
in 1909 for the purpose of securing producta, when little attention was paid to the 
otaheitana peculiar to this valley, although all the hyalina and clara found were 
kept. Therefore the figures for these two valleys give only an approximate indi- 
cation of the true frequency of Ayalina in the local population. 
From table 9 and summary it appears that hyalina contributes only 2.44 per 
cent of the adult Partula population of Tahiti. The figures relating to the partly 
grown snails show that the Ayalina adolescents number 367 out of 7,194, or 5.10 per 
cent. The reason for the difference between the relative numbers of this species 
in adult and immature populations is discussed beyond, when the facts relating to 
fecundity are presented. For the present we may confine our attention to the 
figures for the adult individuals and the percentage of these consisting of hyalina. 
This percentage is far from uniform throughout the island, and the striking differ- 
ences exhibited by various regions and valleys are not only of interest in themselves, 
but they are also of fundamental importance for the study of the larger problems 
under consideration. Specifically, such differences show that in different localities 
this species varies in constitutional vigor quite as surely as it does in morphological 
respects. 
We may first compare the two primary divisions of the island, namely, Tahiti 
nui and Taiarapu. In the former, hyalina forms 2.15 per cent of the population as 
represented by the collections, while in the peninsula the corresponding figure is 
5.31 percent. The data for Taiarapu are rendered somewhat unreliable by various 
circumstances, chief of which is the lack of large and representative collections from 
several valleys. In Aionifaa only 19 adult snails were secured and 4 of these were 
hyalina, thus giving a value for this species of 21.05 per cent; this figure is almost 
certainly misleading. Again, the series of twelve valleys located in the peninsula 
from which collections were obtained is so small, and the ecological conditions vary 
so much in its different quarters, that there are not enough data to serve for a 
thorough analysis of this district. Hence Taiarapu may be disregarded in the 
further discussion of the numerical distribution of hyalina in Tahiti. 
