202 THE ECHINODERMS OF TORRES STRAIT. 
region (5 of these are among the 10 occurring at Mer), but as all of these 10 occur 
on each side of the region and do not occur in the Pacific, there is little reason to 
doubt their occurrence in the strait. Only 5 species in this list occur in the New 
Guinea-New Caledonia region, and only 7 occur in the Pacific further to the east, 
and none of these widespread forms occur at Mer, except the Ophiolepis and Cen- 
trechinus already mentioned and Actinopyga lecanora. On the other hand, 30 of the 
33 forms here listed are East Indian species, and 25 of them extend their range 
southward along the eastern coast of Australia, often to southern Queensland 
and in a few eases to Victoria (Ophiura kinbergi) and Tasmania (Laganum laganum). 
It seems indisputable, therefore, that this Thursday Island group has had a different 
history from the larger Barrier Reef group already discussed. 
There still remain eleven echinoderms whose distribution is such that it has 
seemed better not to include them in the foregoing lists. First there are three 
holothurians (Thyone buccalis and T. okeni, Phyllophorus proteus) and a little brittle- 
star (Ophiothela hadra) which are known from only a few specimens, taken at 
widely separated stations along the coast of eastern Australia. The holothurians 
are very possible endemic species of the Queensland coast. The brittle-star is a 
member of a difficult genus, and its specific identity is in need of elucidation. 
Perhaps these four species might well have been included in list 8. A second group, 
composed of three species (Comatula etheridget, Nardoa tuberculata, Echinometra 
oblonga) occurs on the coast of northwestern Australia and northward to the Aru 
Islands or further, but not in the Torres Strait region. The comatulid, however, 
may be only the young of C. rotalaria; the sea-star is a species easily liable to 
misidentification, and the sea-urchin is of the same sort. Hence the trio may well 
be ignored until more is definitely known about their occurrence on the northern 
coast of Australia. Finally, the four remaining species, two brittle-stars (Ophi- 
arthrum elegans, Ophiopezella spinosa) and two holothurians (Huapta godeffroyt, 
Stichopus horrens), are peculiar in that all occur in the tropical Pacific, also at Mer, 
and in the Thursday Island region, but not any further to the west. Apparently 
these four species belong to the Barrier Reef fauna, but they have pushed their 
way into Torres Strait from the east. 
The grouping of our 292 echinoderms in the above lists brings out clearly the 
fact that the littoral fauna of tropical Queensland is composed of two very distinet 
elements, the larger of which has come in from the east, the smaller from the north- 
west through Torres Strait. If we turn once more to Hedley’s (1910) discussion 
of the “Gulf of Queensland” and the subsequent opening of Torres Strait, we find 
it suggested that when ‘continued subsidence to the east at last burst through the 
Melanesian plateau, a flood of active competitors must have swept in from the 
open Pacific. This reached the Queensland coast either by creeping along the land 
round the Papuan Gulf or by direct, usually larval, transit across the Coral Sea. 
With the opening of Torres Strait and the consequent outgoing current, the Queens- 
land fauna was spread along North Australia to the Moluceas.”’ Three hypotheses 
are involved in these sentences, probably suggested, or at any rate supported, by 
Hedley’s splendid studies on Australian Mollusca: (1) That there was an early 
