204 THE ECHINODERMS OF TORRES STRAIT. 
the Loyalty Islands, or from the Pacific Islands farther east, while 5 are not known 
from the region west and northwest of Torres Strait. It is quite possible that 
alternans does not belong in this Barrier Reef group, since it is not yet known 
from the western Pacific, but I have ventured to put it here because of its absence 
from Australia, except at Port Molle and Mer, and its occurrence at Mer only 
in relatively deep water (18 fathoms) outside the reef. 
The 14 sea-stars represent 10 genera, all of which are widespread in the Indo- 
Pacific region. Of these, however, Astropecten alone has been taken in the western 
half of the Torres Strait region. Culcita and Nardoa are recorded from north- 
western Australia, but it seems very probable that they reached that region with 
the retreating southern coast of the Banda Sea, past Timor, where Asterope also 
occurs. It is particularly noteworthy that half of the 10 genera belong to the 
Ophidiasteridz, and all of these are common at the Fiji-Tonga-Samoan group of 
islands. 9 of these 14 sea-stars are not known from west of the Murray Island 
region, unless it be north of Timor, or in the western part of the Indian Ocean. 
The most striking evidence afforded by the sea-stars, however, in support of the 
Pacific origin of the Barrier Reef group of echinoderms is offered by Nardoa, which 
is a very characteristic New Caledonian genus. At Mer, 4 well-marked species 
(one endemic) occur, and 2 of these are found at Green Island far down on the coast 
of Queensland, but the genus is quite unknown in the western half of the Torres 
Strait region, in the Arafura Sea, or at the Aru Islands. Of course, it is not at all 
unlikely that one or more species will be found somewhere in this extensive area, 
but such a discovery would not invalidate at all the claim that Nardoa has reached 
the Barrier Reef region directly from the Pacific and not from the west. The genus 
Ophidiaster clearly has a similar history, for while 3 species (one endemic) are 
found at Mer, and one of these is found at Green Island, none is known from else- 
where on the Australian coast, from the Arafura Sea, or the Aru Islands. On the 
other hand, one of the Murray Island Ophidiasters was originally described from 
Tonga and another from the Hawaiian Islands. 
The 23 brittle-stars represent but 9 genera, and 4 of these are tropicopolitan 
or more or less cosmopolitan. Nevertheless, there is strong evidence that most, 
if not all, of these 23 species reached the Torres Strait region from the east. The 
Ophiacanthas are too little known and too liable to misidentification to be of any 
importance, but the 4 species of Ophiothrix are characteristically Pacific forms 
and while they occur in the East Indies and even as far west as the African coast, 
they are quite unknown in the Thursday Island region, Arafura Sea, and Aru 
Islands. They are not yet known from the Queensland coast, and if they prove to 
be consistently absent there, which is hardly probable, they must be regarded as 
among the later arrivals from the Pacific. The occurrence of Ophionereis porrecta, 
a brittle-star common at the Hawaiian Islands and elsewhere in the Pacific, on the 
reef-flat at Mer, contrasts markedly with its absence from the Thursday Island 
region, the Arafura Sea, and the Aru Islands, where Ophionereis semoni is a charac- 
teristic form. The distribution of Ophiarachnella septemspinosa is similar to that 
of Ophionereis porrecta. But the family Ophiocomide supplies the strongest 
