44 
TERRESTRIAL MOLLUSCA INHABITING SOCIETY ISLANDS. 
species ; and nowhere else do we find so great a variety of forms in the shape of the 
shells, which varies from the almost globose P. Hebe to the slender P. elongata. It is 
no less noteworthy that nearly one-half of the species have a “ button-like ” tooth on 
the parietal wall, and some have a tooth-like projection on the inner margin of the 
peristome, which gives the aperture an auriculatc shape — a feature found in no other 
group. The Society Islands shells are also the most variable in color, and more than 
half of the species are more or less spirally banded — a character rarely found in the 
cxtra-limital species. y 
The distribution of the various species throughout the group presents many very 
interesting features, which are, indeed, worthy of more attention than I am able to 
give to the subject With three exceptions, each island is inhabited by distinct species, 
and some possess peculiar types or subgenera. The specific centre or metropolis of 
nearly all the species is clearly defined by the profusion or concentration of indi 
vuluals m Imutcd areas. In some instances we find two, rarely three, species havinir 
thcr centre, of distribution in a single valley, and in some eases one is entirely 
restneted to tts he^quarters, whilst the others have spread into two or more valleys 
n lahiti, die largest island m the group, we find eight species only, six of which 
arc endemic. One (P. c/am), which has a limited range, appears to lie graduallv 
lK.ommg extinct. Four species (P .;?/am, no./om, prolaotl Ld ./o/if/a) a^ h 
fact that, notwithstandincr both soeciV. h islands. It is a noteworthy 
Lave not deveioped a Stgk tXrfe^tlmTf 
uniform in ail their specific characters One ’ u ’ a'”''™vy, are reinnrkiiWy 
etcamples of P. ° routliem 
"on (eferwed coral reef,), would have exhibit d temperature and different forma- 
rroin the Tahitian specimer iy ng in 
, ng in d higher temperature on a volcanic 
conditions of life, jttTo^hTvVmT^^^^^^^ the island, and all subject to the same 
typical forms, and the other, which is verv ^ to depart from the 
"’™> '“O"' '"ioties. The above facts w hU Las developed 
-ggest that physical conditions are no he 
“ '•>0 operation of some unknown law ‘ but that it 
Moorca, which is separated from Tahiti bv a cl , , 
bj a channel only eight miles wide, is 
