PARTULA CLARA. 59 
vary greatly in constitutional vigor under almost identical ecological conditions in 
neighboring valleys. 
THE SHELL OF PARTULA CLARA; ITS MORPHOLOGICAL VARIATION AND ITS 
GEOGRAPHICAL VARIATION. 
GENERAL DESCRIPTION. 
The problems of variation, distribution, and evolution are exceedingly involved 
in the case of clara, (a) because the shells present different color characters in the 
populations of various quadrants and valleys, (b) because there are dimensional 
differences in addition to those of color and independent in their variation, and 
(c) because the characters of the unborn young must be treated pari passu with the 
analysis of color resemblances and differences. For these and other reasons it will 
be necessary to enter into much greater detail than in the case of hyalina, although 
as before a general treatment of the whole population will prove useful for certain 
purposes as a preliminary to the detailed analysis of the species, region by region and 
valley by valley. 
My own collections comprise 819 adult specimens of this species and 296 
immature young individuals. Owing to the fragile nature of the shell, more than 
100 adults were unavailable for measurement. ‘The full valley distribution of the 
whole series of mature snails is given in table 18, together with their classification 
on the basis of color, in three divisions of light, dark, and banded groups. 
The morphological characters of 681 measurable shells are summarized in 
table 19. On the whole, this species is quite similar to P. hyalina from Tahiti 
(see table 12) and it varies between essentially the same limits. The aperture is 
distinctly narrower and it 1s also relatively longer as compared with the total length 
of the shell—that is, the spire is more closely coiled than in hyalina. While the two 
species might be confused if only the dimensional characters were taken into account, 
the colors of clara always render it clearly recognizable. The general form and 
color characters of illustrative shells are shown by the valley types of plate 20, figures 
14 to 42, and plate 21, figures I to 31. 
Following the procedure in the case of hyalina, we may next compare the shells 
of the major geographical regions. In Tahitinuithree of the quadrants are inhabited 
to a considerable extent, while in the fourth sector (the northern) only Papenoo is 
occupied; for the present it will be best to combine the shells from Papenoo with 
those of the contiguous eastern sector, instead of taking them by themselves. 
Taiarapu is the fourth major division inhabited. Table 20 shows that the shells 
of the eastern sector are the longest, but they are exceeded in width by those of 
Taiarapu, following the grouped population of the southern quadrant. Because 
the shells of the last-named are so short, on the whole they are the stoutest group 
of the four under consideration. As regards the dimensions of the aperture, the 
eastern and laiarapu shells prove to be almost identical; this correspondence signifies 
a close relationship of the two groups and is further emphasized by the qualitative 
characteristics of color. 
