COMPOSITION AND ORIGIN. yaw 
7. There seems to be a tropical Australian fauna of 64 species, known from both 
the northeastern and northwestern coasts of the continent. It is quite possible 
that this fauna comprises two distinct elements and is not a homogeneous 
group. Until, however, collecting in the Arafura Sea, the Gulf of Carpentaria, 
and along the Arnhem Peninsula has been undertaken, its composition can not be 
discussed profitably. 
8. The Barrier Reef fauna, as revealed by its occurrence at the Murray Islands, 
is a very distinct group, comprising one-fourth of all the 292 forms under considera- 
tion. It is quite wanting from the Thursday Island region. Nearly all the species 
occur in the East Indies, while more than 60 are already known from the islands of 
the Pacific. 
9. The Barrier Reef fauna is replaced in the Thursday Island region by a 
group of some 34 species which seem to have come from the west. A few of them 
have extended their range to the Barrier Reef. 
10. The Barrier Reef fauna seems to furnish strong evidence that Hedley’s 
theory as to the original connection between the Pacific Ocean and the head of 
the ‘Gulf of Queensland” (7. e., what is now the Coral Sea) resulting from the 
sinking of the Solomon Islands ridge, is correct, and that this was followed by an 
influx of Pacific species to the eastern side of the Australian continent. 
11. Detailed analysis of the Barrier Reef fauna shows it to be the direct result 
of this “ Pacific Influx,” and a similar analysis of other groups of species confirms 
the reality and importance of this “Influx” in the formation of the echinoderm 
fauna of eastern Australia. 
12. The study of the echinoderm fauna of tropical Australia west of the Barrier 
Reef area leads to the conclusion that it originated in the main from the East 
Indies with the gradual southward and eastward retreat of the shores of what is 
now the Banda Sea. This retreat finally resulted in the Arafura Sea and the 
opening of Torres Strait. 
13. The opening of Torres Strait led to the eastward and southward extension 
of this East Indian fauna, some representatives reaching the Murray Islands and 
Barrier Reef to the east, and others reaching Port Jackson, and even Tasmania or 
Victoria, on the south. 
14. The evidence is entirely lacking at present for deciding whether the Gulf 
of Carpentaria causes a break in the continuity of the tropical Australian fauna. 
It is quite possible that the echinoderms of northeastern Australia are the result 
of migration along the eastern shores of the extending Arafura Sea, while those 
of northwestern Australia are the forms which long ago occupied the southern 
coasts of what is now the Banda Sea, and have been drawn southwestward with the 
retreat of the Australian coast-line. 
15. There is no satisfactory evidence of any migration of echinoderms west- 
ward through Torres Strait, though it is not impossible that some species from the 
“Pacific influx’? have followed the northern coast of the continent westward. 
Knowledge of the echinoderm fauna of the Gulf of Carpentaria is essential for 
determining this point. 
