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PACIFIC SCIENCE, VoL VIII, July, 1954 
coast of New Guinea, being the most notable. 
Northward and eastward among the low is- 
lands, as conditions become less and less 
favorable for littoral echinoderms, the fauna 
becomes progressively poorer, and segrega- 
tion into definite faunal regions appears to 
become more marked. 
The majority of the Indo-Pacific species are 
small or at most of medium size and are 
present everywhere, though many become 
fewer in individuals among the atolls. In some 
cases the individuals here are noticeably 
smaller. The large species in many cases dis- 
appear or become segregated and confined 
to special areas in which they may become 
differentiated into recognizable subspecies or 
even distinct species. 
The very large and heavy sea stars of the 
family Oreasteridae are especially character- 
istic of tropical coasts, but, except for the 
genus Culcita, the cushion stars, the most 
specialized of the family, ranging from east 
Africa eastward, they are absent from the 
central Pacific area. The largest genus, Penta- 
ceraster, with 14 species, is found from the 
Red Sea and eastern Africa to Australia, New 
Guinea, New Britain, New Caledonia, and 
Samoa, and also on the coast of China, in the 
Philippines, among the Ryukyu Islands, in 
southern Japan, in the Hawaiian Islands, and 
on the west coast of Central America. The 
species found in the Hawaiian Islands and on 
the American west coast are very similar. The 
genus Protoreaster, with four species, ranges 
from eastern Africa to western Australia, New 
Guinea, the Bismarck Archipelago, New Cale- 
donia, the Mariana Islands, the Palau Islands, 
Yap, the Ryukyu Islands, and southern Japan. 
If species of these two or related genera 
occurred among the atolls, they could scarcely 
be overlooked and certainly would be known 
to the natives. 
Among the sea urchins the genus Astropyga 
is characteristic of tropical regions in from 5 
to 88 meters. The species are large, up to 180 
millimeters in diameter. They range from 
eastern Africa to Australia, New Britain, and 
the Hawaiian Islands. One species occurs from 
the Gulf of California to Panama, and another 
is known from off the Dry Tortugas, Florida. 
No species is known from the central Pacific, 
though one may occur there, as there is an 
old specimen in the Copenhagen Museum 
said to be from Nukahiva in the Marquesas;, 
but Dr. Mortensen regards the locality as 
doubtful. Too much faith cannot be. placed 
on the absence of records of this genus, as 
the species seem to be easily overlooked. The 
Caribbean species was not described until 
1934 and is still known only from the four 
original specimens. 
Among the brittle stars, the very large and 
conspicuous basket stars of the family Gor- 
gonocephalidae, otherwise cosmopolitan, have 
not been reported from the small islands, nor 
have any of the species of Trichasteridae, with 
many-branched arms. However, the species 
of these two families occur in water of from 
a few fathoms downward, not along the 
shores, so, although they are frequently 
brought up on fishermen’s lines, the ab- 
sence of records is not necessarily significant. 
Among the more conspicuous and char- 
acteristic of Indo-Pacific sea urchins are the 
limpet, pavement,” or helmet urchins of the 
genus Colobocentrotus . These are of fairly large 
size and live in the surf zone, usually in large 
colonies, so that they are not easily over- 
looked. One species, C. atratus, occurs at 
Zanzibar, Natal, Madagascar, Mauritius, the 
Seychelles, Christmas Island, Java, Timor, and 
Amboina, and also in the Hawaiian Islands, 
though not between the Moluccas and Ha- 
waii. A related species, C. pedifer, is confined 
to the Tuamotus. A third species, C. mertensi, 
is found in the Bonin and Mariana Islands. 
A related genus with normal instead of modi- 
fied spines, Zenocentrotm, occurs in Tonga and 
Samoa. The latter, first described in 1931, 
may have a more extended distribution as it 
is easily confused with sea urchins of other 
families. 
Among the largest, most conspicuous, and 
most characteristic of the Indo-Pacific sea 
