58 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
Partula clara resembles other species of the genus in its food habits, in its 
arboreal nature, and in its susceptibility to changes of moisture. It crawls more 
rapidly than other forms, with the possible exception of hyalina. No special nurse- 
plant is favored, although the herbs and bushes upon which it is found in greater 
abundance during the daytime may differ in various localities. 
NUMERICAL DISTRIBUTION OF PARTULA CLARA. 
In the case of hyalina, a full discussion was given of variations in numerical 
distribution, and of the interpretation and significance of such variations. Having 
this as a basis, it will be unnecessary to treat the present case in extenso; only the 
salient points of agreement and of difference need to be established. 
The census tables (tables 9 and 18) enumerate the valleys belonging to the con- 
tinuous area occupied by clara, together with the percentage values of this species 
in the several valley populations; the chart (text-fig. 5), to be described at a later 
juncture, illustrates in graphic. form the extent of the area now inhabited by this 
species as well as the territory formerly occupied. The first point to be noted is that 
clara does not occur in the northwestern part of Tahiti nui—that is, between Punaruu 
Valley and Papenoo Valley. This area of absence is relatively drier than the area of 
presence, and therefore the lower degrees of moisture in the former seem to be 
limiting conditions to the horizontal spread of this form. We may recall the fact 
which was duly emphasized earlier, that hyalina was most abundant relatively in 
the very area from which clara is absent. The two species appear to be exactly 
opposite in their general relations to moisture. 
Summarizing the facts by quadrants, and including Papenoo as an element of 
the eastern quadrant, it appears from table 18 that the southern and lower western 
areas are on the whole more favorable habitats for clara. The paucity of individuals 
in the eastern valleys is due to the recent spread of this species into that sector. 
Taiarapu has also been populated by clara at a relatively recent date, although 
earlier than the eastern sector. 
It is impossible to discern a relation between relative abundance and an ecologi- 
cal peculiarity of valleys inhabited by clara, like that between dryness and the 
frequency of hyalina. Owing to the recent spread of clara into areas outside of its 
ancient territory (the southern quadrant), only this should be considered. Vaira- 
haraha and Vaihiria are valleys of the first order of size, and in their populations 
clara forms 27.77 per cent and 23.23 per cent respectively. But in Temarua and 
Papeiti, also of large size and relative dryness, this species constitutes only 0.87 per 
cent and 1.84 per cent of 573 and 488 adults in the representative collections. The 
second-order valleys vary from 0.60 per cent (Taharua) and 0.66 per cent (Apirimaue) 
to 20.42 per cent (Tereehia). Similarly the smallest valleys vary from 1.44 per 
cent (Maara) to 8 per cent (Teohu). These last are much more humid than the 
larger valleys; hence they ought to furnish higher percentages of clara if greater 
wetness materially fosters the numerical increase of this species. The facts do not 
support this contention. In short, we must conclude that the several valley colonies 
