214 
Guam, and Japan, are all centers with which 
the Micronesians and Japanese had intensive 
commerce. The frequent devastation which 
many atolls including XJlithi experience in ty- 
phoons suggests that such atolls may have their 
land snail faunas periodically much reduced if 
not obliterated. If we may assume that this hap- 
pened on Mogmog in 1906, then it follows that 
all the species of snails found in 1945 arrived 
between those dates. 
Recently I proposed several hypotheses as 
criteria which may be useful for recognizing 
exogenous nonmarine mollusca of a given fauna 
(Harry, 1964). These criteria were derived from 
my experience with the nonmarine mollusca in 
temperate North America, and the freshwater 
mollusca of the Antilles. To what extent they 
will suffice in the islands of the Pacific has yet 
to be determined, but we may review them in 
regard to the snails of Ulithi. 
We can be absolutely certain that a snail is 
introduced into a given area only if it is known 
that the species was not present in the fauna 
prior to a certain date, and by having first hand 
knowledge of the time and method of its in- 
troduction. Unfortunately, such information is 
rarely available. In the Pacific islands, Achatina 
fulica is almost the only example. It is notable 
that this snail is not known as yet from any 
atoll, although it lives on the coastal area of 
some high islands, such as Saipan, where 1 col- 
lected it in 1944. In most cases, circumstantial 
evidence must be relied on to evaluate a given 
species as being exogenous. 
Most tourist snails have a wide geographic 
distribution. In the case of the present fauna, all 
of the species are known to occur on at least 
one other island, and for some a very extensive 
range has already been recorded. There is more 
of such data for the pulmonates than for the 
prosobranchs, because the prosobranchs have re- 
ceived much less systematic study. All but the 
Pyihia and the slug ( Vaginulidae) are small in 
size, and this might have the double advantage 
of allowing them to be easily concealed and 
transported both as eggs and as adults. It is a 
singular fact that of nonmarine mollusca, at 
least, the tourist species of very largest size 
are nearly always introduced deliberately, and 
PACIFIC SCIENCE, Vol. XX, April 1966 
usually for food (some Helicidae, Achatina 
fulica, Ampullariidae; see Harry, 1964). But 
snails of intermediate size, as Rumina, Brady- 
haena, some Lymnaeidae, and perhaps Pythia 
and the slug of the Ulithi snails, are to be 
grouped with the microfauna, since they are 
only Introduced by man accidentally into new 
areas. Pilsbry ( 1900') has made the Interesting 
observation that, although regions outside the 
Pacific area have contributed terrestrial snails as 
tourists to the Pacific islands (e.g., Gulella and 
Lamellaxis of the Ulithi list), those islands have 
in turn provided no member to the list of tourist 
snails of other parts of the world. This state- 
ment is valid only if we speak of the Indo- 
Pacific Islands rather than merely the Pacific 
islands s.s. Nevertheless, the accidental dissemi- 
nation of land snails by man within the Pacific 
area is probably greater than has been previ- 
ously recognized. 
Tourist snails tend to remain in an environ- 
ment highly modified by man, and do not, 
through their own natural ability, invade the 
more natural surrounding areas. This principle 
is probably as valid for introduced snails as It 
is for other introduced organisms (Bates, 1956: 
788). Thus, man not only is the agent of Intro- 
duction, but also is responsible for maintaining 
the environment which allows them to become 
established in their new locality. At least the 
biotic environment of atolls such as Ulithi, 
which are under coconut cultivation, are man- 
effected situations. Much more ecological work 
needs to be done on atoll snails to investigate 
the second part of this hypothesis. Probably 
there are ecological divisions to be recognized 
among different atolls, even though superficially 
their biotas appear very much the same. 
There are relatively few species of tourist 
snails (generally so recognized) which are com- 
mon to the several low and intermediate islands 
which have been most intensively studied: of 
the 17 snails found on Ulithi, only 1 species Is 
recorded among the 22 of Makatea (C M. 
Cooke, 1934), only 2 occur among the 11 on 
Rongelap (Reigle, 1964), and only 2 occur 
among the 11 on Funafuti (Hedley, 1899). 
None of the islands cited has more than a few 
species In common. This may be due In part 
to diverse patterns of human movement among 
