rm a
peculiar genus of geckoes, but both its locality and affinities appear to
be somewhat doubtful.

_Land-shells._--The only other group of animals which has been carefully
studied, and which presents features of especial interest, are the
land-shells. These are very numerous, about thirty genera, and between
three and four hundred species having been described; and it is remarkable
that this single group contains as many species of {317} land-shells as all
the other Polynesian Islands from the Pelew Islands and Samoa to the
Marquesas. All the species are peculiar, and about three-fourths of the
whole belong to peculiar genera, fourteen of which constitute the subfamily
Achatinellinae, entirely confined to this group of islands and constituting
its most distinguishing feature. Thirteen genera (comprising sixty-four
species) are found also in the other Polynesian Islands, but three genera
of Auriculidae (Plecotrema, Pedipes, and Blauneria) are not found in the
Pacific, but inhabit--the former genus Australia, China, Bourbon, and Cuba,
the two latter the West Indian Islands. Another remarkable peculiarity of
these islands is the small number of Operculata, which are represented by
only one genus and five species, while the other Pacific Islands have
twenty genera and 115 species, or more than half the number of the
Inoperculata. This difference is so remarkable that it is worth stating in
a comparative form:--

Inoperculata. Operculata. Auriculidae.
Sandwich Islands 332 5 9
Rest of Pacific Islands 200 115 16

When we remember that in the West Indian Islands the Operculata abound in a
greater proportion than even in the Pacific Islands generally, we are led
to the conclusion that limestone, which is plentiful in both these areas,
is especially favourable to them, while the purely volcanic rocks are
especially unfavourable. The other peculiarities of the Sandwich Islands,
however, such as the enormous preponderance of the strictly endemic
Achatinellinae, and the presence of genera which occur elsewhere only
beyond the Pacific area in various parts of the great continents,
undoubtedly point to a very remote origin, at a time when the distribution
of many of the groups of mollusca was very different from that which now
prevails.

A very interesting feature of the Sandwich group is the extent to which the
species and even the genera a