316 
PACIFIC SCIENCE, Vol. XI, July, 1957 
live embedded in coral, and their shells be- 
come adapted to the configuration of the 
narrow cavities in which they reside. Thus the 
only consistent means of recognition is the 
difference in external sculpture. The sculptur- 
ing is, however, commonly obscured by en- 
crustations, and consequently it is difficult to 
distinguish one species from the other. 
Quoyula madreporarum (Sowerby, 1834). 
Tinker (1952) p. 104, 3 figs, on p. 105 [as 
Rhizochilus madreporarum Sowerby]. 
Micronesian specimens are characteristic- 
ally 0.5 to 0.75 inch long, but Elawaiian speci- 
mens attain lengths of 1.25 inches. Shell 
whitish with a purple aperture. 
Q. madreporarum lives embedded in pocket- 
like depressions on coral. It is ordinarily 
found a few feet below low tide line on small 
lagoon reefs or on seaward reef flats. It ap- 
parently lives exclusively on living coral and 
commonly on branching species. Specimens 
in the present collections were found on spe- 
cies of Stylophora , Pocillopora and Montipora. 
Encrustations on the shells of both Q. madre- 
porarum and Q. monodonta make them difficult 
to distinguish from their coral substrate. 
GEOGRAPHIC range: Apparently limited to 
the Pacific. USNM records are from southern 
Japan, the Caroline, Marshall, and Hawaiian 
islands, and from Johnston Island and Pearl 
and Hermes Reef. Uncommon in Micronesia. 
Quoyula monodonta (Blainville, 1832). 
Hirase and Taki (1951) pk 111, fig. 14. 
Characteristically about one-half inch long 
and whitish with a purple aperture. Perfect 
specimens possess a single tooth at the base 
of the columella. 
Q. monodonta lives in pocketlike depres- 
sions on coral. The recent Micronesian col- 
lections indicate that it occurs exclusively on 
living coral, typically on branching species 
such as Pocillopora , Seriatopora , and Stylophora , 
and on branching forms of Porites. It is most 
commonly found on small reefs in lagoons or 
protected harbors, from slightly below low 
tide line to depths of 30 or 40 feet, but it has 
also been taken on seaward reef flats, just 
shoreward of the reef edge. At Ifaluk, speci- 
mens were found with egg cases enveloped 
under the foot. 
GEOGRAPHIC range: USNM records are 
from the Red Sea and Ceylon in the Indian 
Ocean eastward through the Pacific beyond 
the Hawaiian and Tuamotu islands to the 
coast of Lower California at Cape San Lucas, 
Acapulco, and Espiritu Santo Island; and also 
from the Philippine and Mariana islands south 
to Queensland, Australia, and the Loyalty 
Islands. Reported from southern Japan. Very 
common in Micronesia. 
Genus Magilus Montfort, 1810 
Magilus antiquus Montfort, 1810. 
Fig. 25. Magilus antiquus Montfort. Composite 
drawing of two specimens from Saipan, Mariana Is- 
lands (USNM 595414). 
M. antiquus is a molJusk of curious behavior 
and specific habitat. It begins life as a free- 
living gastropod with a symmetrically shaped 
shell but soon settles upon living coral, be- 
comes embedded, and develops an extraor- 
dinary shell. As the coral grows, M. antiquus 
secretes a tubelike extension of its aperture. 
It stops up its original shell with calcareous 
material, then vacates it, and lives in the free 
end of the tube, which extends to and opens 
upon the surface of the coral. It is not known 
