IO0O VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
sutural band, the darker general ground-color, and the indistinctness of the band 
are characters which ally the two groups and separate them from all other colonies 
whose members are exclusively or predominantly dextral. The variety /eva is 
undoubtedly a product of some original stock of nodosa, but its dextral components 
seem to be secondarily derived from peculiarly colored and reversed antecedents. 
Partula nodosa exigua var. nov.—Atehi Valley. 
Atehi or Hapaa Valley is a small gorge running parallel with Maruapoo about 
0.75 mile to the south. Its mouth is separated by wooded ridges from the openings 
of Maruapoo and Papehue. On entering the valley, the floor rises rapidly, being 
450 feet in barometric level at 0.75 mile. ‘The stream runs in a steep-walled gorge, 
as in the lower part of Maruapoo. On account of the ruggedness of the region, 
efforts to collect the snails from Atehi and Maruapoo were more arduous than 
anywhere else in Tahiti. 
Out of 450 adult snails of all species only 4 specimens of nodosa were secured in 
the course of two journeys into Atehi Valley. This small number is remarkable in 
view of the proximity of Maruapoo and Papehue, in both of which nodosa figures 
largely. Yet even more astonishing is the wide divergence of these 4 specimens 
from the shells described earlier; were it not for somewhat similar individuals of 
the Papehue colony, the Atehi examples would be justly denominated a separate 
species! 
Tas_e 47.—Partula nodosa exigua. Atehi Valley. 
STATISTICAL CHARACTERS. 
Coe Tooru. FECUNDITY. 
Character. Mean value. ais 
deviation. 
Shell, length, mm...........| 14.0750 .2225 | 0.4918+ .1573 || Trace........... ON RRecordsseprierereerere 4 
widthyem merrier 8.8500 .0559 SOEIES OOS ||| WeOUNssooonncncc 3 ||| Grew coocongcu00 4 
proportion, per cent...} 62.7500 .6021 | 1.7853 .4258 |} Large tooth...... 1 
Very large tooth..| 0 || Eggs.............. 4 
Aperture, length, mm....... 7.7500 .0876 .2598= .0619 | Young!............ 6 
width sm merrier 5.8500 .0559 SIOERIES (OSS |!| WOES doocuouoos 4 
proportion, per Total contents..... 10 
Cente ethceseren 76.00001.1316 | 3.3556 .8002 
Average for gravid 
Length aperture + length andwormallemnrence 2.5 
shell, proportion......... 54.5000 .5841 | 1.7320 .4130 
1A]l plain and dextral. 
The 4 shells (figs. 7 to 10, plate 24) are very small, dextral, and unbanded; their 
reduced size warrants the use of the term ex7gua as a varietal distinction. In ground- 
color they are uniform brown, from dark to chocolate, and the apices of all have a 
purplish tinge. The nodosity on the columellar border of the aperture is evanescent 
in 2 specimens and absent in the other 2. In surface sculpturing and in the character 
of the whorls they agree with dextral examples of true nodosa existing in valleys to 
the south; they differ absolutely from the solid brown type of P. otaheitana with a 
sinistral coil which inhabits Atehi. The other dextral specimens from this valley 
belong to P. hyalina and P. clara, with which the four examples under consideration 
can not possibly be confused. 
