Fauna and Flora of New Zealand. 431 
The distribution of the marine Mollusca of Australia and 
Polynesia is favourable to Mr. Wallace’s theory; but’ the 
terrestrial Mollusca, although most nearly allied to those of 
the Indian archipelago, have strong affinities with the Mol- 
lusca of South America, and show no connexion with those of 
Africa. This is seen in Trochomorpha, Tornatellina, Cyclo- 
tus, Cyclophorus, and Helicina, which are found in Polynesia, 
Australia, and South America ; Macrocyclis, in Australia and 
South America; Partula (a characteristic Polynesian genus) 
is found also in South America; Placostylus is allied to Ortha- 
licus of Chili, Peru, and the Solomon Islands; and Vaginulus, 
a marine pulmonate, occurs in India, the Philippines, and in 
South America. This remarkable distribution is very instruc- 
tive; for as the marine shells of the Indo-Pacific province 
have been unable during the whole of the Tertiary era to cross 
from Polynesia to America, it follows that when the ancestors 
of these land-shells crossed, the physical geography of the 
region must have been very different trom what it is now, for 
there is no trace of their having passed into South America 
from the north. 
We see, then, that the Australian fauna consists of three 
elements. The first is typified by the mammals, and is cha- 
racteristically Australian. The second is typified by the birds, 
and is more nearly related to African than to American forms. 
The third is typified by the frogs, and is more nearly related 
to South America than to any other partof the globe. There 
is also a fourth element—the antarctic—which I pass over for 
the present. 
Now it is very difficult, or even impossible, to believe that 
all the groups of semitropical plants and animals which con- 
nect Australia, Polynesia, and even the Sandwich Islands 
with South America have travelled down from the north by 
the present land-routes, for then we should have to suppose 
that all had become extinct in North America, and certainly 
we should expect to find the connexion between Australia 
and Africa at least as close as it is between Australia and 
South America, which is not the case. But even if we got 
over this difficulty, we should still be unable to explain the 
facts. If, for example, the frogs had passed into South 
America by the same route as the birds, both would have 
shown a similarity in their distribution. The assumption 
that the present frogs are mere relics of a formerly more 
extended distribution, and that allied groups have become 
discontinuous through extermination, will not help us; for if 
all birds were now to become extinct north of the equator, we 
should still find the avifauna of Australia more nearly related 
to that of Africa than to that of South America; and it is 
