212 THE ECHINODERMS OF TORRES STRAIT. 
CONCLUSIONS. 
When the composition of the rich echinoderm fauna of Torres Strait is carefully 
examined, its origin is indicated with surprising clearness, and the physiographical 
history of northern Australia is illuminated to a greater degree than might have 
been expected. During Mesozoic times, the eastern coast of Queensland possessed 
either no echinoderm fauna or so scanty a one that there are no survivors to-day. 
The northern coast of the western part of the continent possessed a fauna essentially 
East Indian in its composition. The depression of land areas in the region east of 
New Guinea led finally to the connection of what is now the Coral Sea with the 
Pacific between the Solomon Islands and the New Hebrides, and this connection 
has become more and more extensive with the passage of time, until the contours 
of the present day have been reached.! At the same time, the coast-line of tropical 
Australia has retreated westward and the Great Barrier Reef has been formed. 
With these physiographical changes came an influx of echinoderms from the Pacific, 
following the northwestern coast-line of the new straits and seas and giving rise 
finally to the rich echinoderm fauna of the Murray Island region and the Barrier 
Reef, and to some extent to that of southern Queensland and New South Wales. 
The changes taking place to the northwest of the Coral Sea and to the southeast 
of the Banda Sea finally led to the formation of Torres Strait with the result that 
the East Indian fauna now had direct access to the northeastern coast of Australia, 
and many of its echinoderms migrated eastward and southward to mingle on the 
Queensland coast with the species of the Pacific influx. The striking differences, 
even at the present day, between the echinoderms of the Thursday Island region 
and those of the Murray Islands suggest that the East Indian fauna reached the 
vicinity of Thursday Island, occupying the Arafura Sea and western end of Torres 
Strait before the connection with the Coral Sea was established and has not as 
yet been greatly affected by the completion of the Strait. On the other hand, a 
considerable number of its component echinoderms have reached the Murray 
Islands and the Barrier Reef, adding much to the richness of the fauna of that 
region. The echinoderm fauna of the eastern coast of Australia is thus made up 
from the mingling of the Pacific influx around eastern New Guinea with the East 
Indian influx via Torres Strait, the former apparently being the more important 
of the two. Whether the fauna of southern Australia and Tasmania has developed 
from this mingled stream, or whether a new source is concerned in its formation, 
are questions of the greatest interest, but quite outside the scope of the present report. 
1It is not intended to even imply that there has been a consistent and continuous sinking of this area since 
the Mesozoic. There may have been several periods of elevation alternating with periods of depression. That ques- 
tion simply does not concern us in the present report. 
