Land Snails of Ulithi Atoll, Caroline Islands: 
A Study of Snails Accidentally Distributed by Man 
Harold W. Harry 1 
During the Second World War I had oc- 
casion to visit briefly on Mogmog Islet, Ulithi 
Atoll, Western Caroline Islands, and to collect 
the land snails reported herein. The collection 
was divided, and one part, including all speci- 
mens of several less abundant species, was sent 
to the late Dr. C Montague Cooke, Jr. of the 
Bernice P. Bishop Museum. In unsorted "sweep- 
ings” he found a few species which I had over- 
looked. It was his intention to publish the data 
in a paper on comparative faunal studies of the 
Mid-Pacific Islands, but death intervened. Some 
years later I had the opportunity to study more 
carefully the set I retained, using the extensive 
collection and library at the University of Michi- 
gan Museum of Zoology. More recently, a grant 
from the National Science Foundation ( NSF 
GB-2753) has made it possible to complete the 
study. 
The collection is significant in several ways. 
Although there have been very few papers on 
the nonmarine mollusca of the Pacific atolls, 
this fauna seems to be larger than any previ- 
ously reported (Hedley, 1899; Pilsbry, 1900; 
Reigle, 1964; and the bibliography of the latter 
paper). Most if not all of the species are dis- 
seminated by man, thus providing not only an 
antithetical example of a fauna of high endem- 
icity, but also shedding new light on the vex- 
ing problem of zoogeography of the land snails 
of the I ndo Pacific area. The pitifully slow rate 
at which data on the Indo-Pacific land snails 
have accumualted has been due in large part to 
the inadequate descriptions and lack of illustra- 
tions of many species. The present study af- 
forded opportunity to illustrate and redescribe 
several species thus neglected. Moreover, two 
species have interesting growth patterns which 
have not been previously reported, but which 
are of systematic importance. 
1 Texas A&M University Marine Laboratory, Gal- 
veston, and Rice University, Houston, Texas. Manu- 
script received February 23, 1965. 
Mogmog Islet is one of several which inclose 
the lagoon of Ulithi Atoll. The closest islands 
to Ulithi (10° 5' N, 139° 43' E) are Fais, 45 
miles to the east; Yap, 110 miles westward; and 
Guam, 400 miles to the north. Between World 
War I and World War II these islands had 
been a Japanese protectorate, as were the Mari- 
anas north of them, and the Palau Islands to 
the west. Several hundred Micronesians who 
called Mogmog home had been evacuated at the 
time of my visit. Writing at the turn of the 
century, Christian ( 1899: 18-20) noted that 
there was a tradition of annual commerce be- 
tween the Caroline Islands and Guam, carried 
on in native canoes. Also, the natives of Yap 
and Peleliu (in the Palau Islands) "used to go 
on long voyages of trading and conquest,” and 
the natives of Ulithi "have from ancient times 
been subject to Yap, and they come down every 
February to pay them tribute.” 
Much of Mogmog Islet, which is only a few 
acres in extent, had been cleared of undergrowth 
when I visited it in August 1945. It was then 
being used as a recreational area for U. S. Navy 
personnel. The seaward margin of Mogmog is 
about 8 or 10 ft above the beach, which it fronts 
precipitously. From this meager elevation the 
land slopes gently down to the lagoon. Along 
the outer edge of the islet was a narrow strip 
of land on which the undergrowth was left rela- 
tively undisturbed. This zone was covered with 
large chunks of loose coral rock. The land snails 
were picked from the organic mulch which had 
collected between them. Near the center of 
Mogmog was a depression of about l /i acre, in 
which grew several species of emergent fresh- 
water plants. The surface of this pond had been 
heavily oiled. 
Besides the snails which I collected, a num- 
ber of other land animals were in evidence. A 
species of terrestrial flatworm was abundant, 
and there was one species each of an isopod, a 
millipede, and a centipede. Of insects, I noted 
212 
