208 THE ECHINODERMS OF TORRES STRAIT. 
movements of the Pacific fauna would be obliterated. If, however, certain species 
moved along the northern coast of Australia, their absence from Timor and the 
Aru and Kei Islands might be indicative of their history. Were it not for the Fly 
River delta, it would be absurd to expect any difference between the echinoderm 
faunas on the northern and southern shores of western Torres Strait and the Arafura 
Sea, but the presence of that delta undoubtedly put a stop to any westward move- 
ment of the Pacific influx of echinoderms along the southern coast of New Guinea. 
Hence such a movement might occur, confined to the northern coast of Australia. 
When, however, we study the distribution table (p. 192), we find there are relatively 
few species which occur on the northwestern and northern coasts of Australia, 
west of Torres Strait, which are also found in the Fijian or Samoan regions, and 
of these not half a dozen are lacking from the northern side of the Arafura Sea. 
There seems to be, therefore, no adequate evidence that the opening of Torres 
Strait has resulted in any movement of echinoderms westward or northwestward. 
The Pacific influx seems to have been turned almost wholly southwestward and 
southward by some influence, probably the fresh-water drainage of southern New 
Guinea, which has given rise to the Fly River and its delta. As a result of this, 
the opening of Torres Strait has made little difference, if any, to the echinoderm 
fauna west of it. Its influence on the Murray Islands region to the east has been 
somewhat more evident, as 40 of the 156 species occurring there seem to have 
reached the islands from the west. 
In contrast, then, with the results obtained by Hedley from his study of the 
molluscan fauna, this study of the echinoderms of the Torres Strait region gives 
no evidence in support of either the hypothesis that there was an ancient ‘“ Gulf 
of Queensland” with a characteristic marine fauna, or the hypothesis that with the 
opening of Torres Strait the marine fauna of the Queensland coast passed westward 
and northward to the southern Moluccas. This absence of evidence in favor of 
these hypotheses may be accounted for by the interesting hypothesis that there 
were no echinoderms in the old Gulf of Queensland, but that echinoderms first 
reached eastern Australia with the Pacific influx. Whether or not the evidence 
afforded by the fossil echinoderms of Australia gives support to this theory is a 
matter worthy of investigation. In no better way can the probability of the 
hypothesis be established, or perhaps its absurdity be shown. But the evidence 
from fossils may not be discussed here. 
The hypothesis of Hedley, that the connection of the Pacific with the Coral 
Sea by the depression of the Solomon Ridge brought a great influx of species to the 
Australian coast, is amply demonstrated by the Torres Strait echinoderm fauna, 
and this hypothesis may perhaps be now regarded as a reasonable conclusion. 
THE TRIPLE ORIGIN OF THE COASTAL FAUNA OF TROPICAL AUSTRALIA. 
Aside from the light which these studies have thrown on the hypotheses of 
Hedley, they have made fairly clear the triple origin of the echinoderm fauna of 
tropical Australia. Of course, in one sense, this fauna is a unit derived from a 
single source. It is essentially an Indo-Pacific fauna and there is little doubt that 
