gO VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
list of Polynesian land-shells, he wrongly assigns 1t to Moorea. Dr. Pfeiffer gives Tahiti 
and the Navigator Islands as its habitat. The type is purely Tahitian and does not occur 
at the latter group. . . . About one in two hundred is sinistral. Bandless varieties are 
not infrequent, and some are fulvous or light chestnut brown, with a pale narrow sutural 
band.” 
The first point of importance is that the range of P. nodosa is now far wider 
than it seemed to be in Garrett’s time. ‘This may signify a recent spread of the 
species or it may mean only that Garrett confined his explorations in the western 
quadrant to Punaruu Valley, designated by the name of its district. Both supposi- 
tions are correct, inmyopinion. Probably Garrett did not explore fully the smaller 
gorges adjacent to Punaruu, like Maruapoo and Atehi; and it is possible that he 
gave little attention to Taapuna on the north, or to Papehue and Aoua to the south, 
for he does not mention these localities specifically. But it is certain that he 
studied the snails of Orofere, for he correctly described the varieties of P. otaheitana 
existing in that valley, which he designated by a nowobsolete name. Furthermore, 
nodosa was not taken by me in 1907 in Orofere Valley, while in the following year I 
found a few individuals in exactly the same locality which was visited earlier. Hence 
it is fair to conclude that P. nodosa has spread recently from a small area of former 
occupation, although this may not have been as restricted in Garrett’s time as that 
investigator supposed. 
Considering now the varying frequency of this species in the different valleys 
of its territory, a striking feature is the small collection from Atehi, 4 out of 450 
adults. This can not be due solely to the small size of the valley in question, for 
Maruapoo is almost as small, but 84 per cent of its 945 adults belonged to nodosa. 
Again, the abundance of P. otaheitana in Atehi proves that it is a favorable habitat 
for Partule. It does not seem likely that the species has only recently established 
itself here, an explanation which must be adopted for the small numbers in Orofere; 
it would seem rather that P. nodosa was formerly more abundant in Atehi and that 
it had decreased in numbers and relative frequency, owing to inherent weakness, as 
in the case of many colonies of P. hyalina and P. clara. 
The next general point of note is that sinistral adult snails occur in collections 
from Taapuna and Maruapoo and that they far outnumber the dextral individuals 
in the latter instance. For one reason and another, a larger series could not be 
secured in Punaruu; and as Garrett states that only 1 in 200 from this valley 
was sinistral in his time, the non-occurrence of such shells in my collection of 290 
individuals of all ages can not be regarded as satisfactory evidence of their com- 
plete absence from this valley at présent; certainly, however, the reversed type has 
not increased in relative numbers during recent decades. 
THE REGIONAL VARIATION OF THE SHELL OF PARTULA NODOSA. 
Passing now to the detailed description of the species, we will take up the several 
colonies, valley by valley, in order to distinguish the collective characteristics that 
give the peculiar complexion to the group of each locality. The distinctive colonial 
character in any instance is determined by (1) the proportionate numbers of this 
species in the population of the valley, a matter duly noted earlier; (2) the propor- 
