PARTULA NODOSA. 105 
is no doubt that the area from which the snails were secured in 1908 was actually 
visited in the prior year, and while Orofere may have been invaded by immigrants 
from Aoua as early as 1907, it is significant that no individuals of the species were 
present in a collection comprising 185 snails of all ages, when one year later 18 out 
of 92 adults and ro out of 22 adolescents were nodosa. As Garrett describes cor- 
rectly the variety of P. otaheitana existing here, specifying the valley by an old name, 
and as he states expressly that nodosa was found by him only in Punaruu, we are 
justified in concluding that the Orofere colony of nodosa has been founded only in 
the most recent years. 
Seventeen of the adult shells are assignable to Class II (fig. 36, plate 24), while 
' the single plain specimen is a small example of Class I (fig. 35, plate 24). All possess 
a pillar tooth of average size. Only three were gravid, and each one bore a single 
egg; hence there are no data on heredity. The statistics (table 52) are not especially 
noteworthy in themselves, but are valuable for the inter-valley comparisons. 
TasBLeE 52.—Partula nodosa intermedia. Orofere Valley. 
Mean VALUE. 
Shell. Aperture. Length aper- 
a ene eerie ee ee eee aed Pak |e eye eal ty dees 2 |) turesength 
Group. No shell, propor- 
Length. Width. Proportions. Length. Width. Proportions. tions. 
mm. mm. p. ct. mm. mm. p. ct. p. ct. 
Banded’........ 17 | 15.4911 .1814) 9.3588 .0957| 60.3824 .2963) 8.3353+.0967| 6.6764 .0800) 80.0294 .3554) 53.7353+.2663 
elainversveveyes|:-ys 1 3225 OO Reerees| Sol OO OMmmrrrys| KOO. OC OMe |e. 0 OOM rao: OOO Memes rl Oso OOO o4-0000 
PAM Py aveheas sys ioxsis ue 18 | 15.3667+.1899) 9.2889+ .1014) 60.3889+ .2798) 8.2778+.0988) 6.6111+.1018| 79.8333+.3594| 53.7778+.2531 
STANDARD DEVIATION. 
17 1.1088 = .1283) 0.5851+.1677| 1.8111+.2095) 0.5910+.0684! 0.4893+.0566 2.1725+.2513) 1.6280+.1883 
18 1.1945 = .1343) .6376+.0717) 1.7603+.1978, .6214+.0699| .6402+.0720| 2.2608+.2541] 1.5918+.1790 
SUMMARY AND CONCLUSIONS. 
Having dealt in severalty with the colonies of P. nodosa, it now remains to 
consider the species as a whole and to formulate the conclusions which may be 
drawn from the summarized details. Always with due regard to the distinction 
between the facts themselves and the interpretations of the observations, four 
general topics are to be discussed, namely, the range of the species as a whole, the 
variation of the species within its range, the genetic history of the distinguishable 
varieties, and the factorial value of internal and external causes of differentiation. 
I. Partula nodosa now inhabits seven valleys in the western quadrant of Tahiti 
nut, having extended its range to some degree in recent years. The grounds for this 
statement have been discussed at some length in earlier pages, but additional 
aspects of the evidence demand further consideration. The fundamental datum is 
that the species occupies a compact sector comprising 7 valleys in a definite part 
of Tahiti; hence, in the series of Tahitian species arranged according to the extent 
of the territory inhabited, Partula nodosa stands between the extreme species, 
