COMPOSITION AND ORIGIN. 209 
that fauna originated in the East Indies; but in a different sense the tropical Aus- 
tralian fauna is the result of three independent movements, and hence we may 
fairly refer to its triple origin. 
1. The Original Fauna: The evidence at hand indicates that the first Australian 
echinoderms occurred on the northern coast of the continent, and apparently at 
a time when there were few, perhaps no, echinoderms on the eastern coast. Without 
going into the question of the topography of what we now call the East Indies, 
as they existed during Mesozoic and early Tertiary times, there is little reason to 
doubt that while New Guinea and Australia were still united as one land-mass, a 
bay of the Indian Ocean lay to the northwest of what is now Torres Strait, its 
southern limit being the then northern boundary of Australia. Bathymetrical 
charts seem to indicate that this bay occupied what is now the Banda Sea, and that 
with the passage of time its shores have steadily receded southward and eastward, 
and by a final eastward extension, union with the Coral Sea through Torres Strait 
was effected. The echinoderms occupying the southeastern shores of this bay 
or sea formed the first echinoderm fauna of Australia, undoubtedly East Indian 
in its origin and Indo-Pacific in its composition. It still forms a considerable part 
of the fauna of northern Australia west of the Gulf of Carpentaria, and is largely 
the source of the fauna of tropical West Australia. Most of its components passed 
into the Torres Strait region and many, ultimately, clear through to the Barrier 
Reef and southward along the Queensland coast, but a few have merely held their 
ground and remain to show what this early fauna was like. The following may be 
mentioned as some of the characteristic species of this fauna. 
Comatula etheridgei.' Nepanthia brevis. Heterocentrotus mamillatus. 
Nardoa tuberculata. Ophiothrix melanosticta. Peronella orbicularis. 
Hacelia helicosticha. Ophiothrix striolata. Pseudocucumis africanus. 
Ophioplocus imbricatus. 
It is obvious, from the unsatisfactory nature of this list, that few of the species 
occurring in the original fauna have failed to follow the extending shore-lines as 
Torres Strait opened. Probably Ophioplocus and Heterocentrotus have failed to 
pass through Torres Strait at all, and their occurrence at Mer is due to the Pacific 
influx. If this is the case, they are admirable representatives of the first Australian 
fauna. It may perhaps be worthy of note that they are both highly specialized, 
but very widespread forms. 
2. The Pacific Influx: This has been so fully discussed in the preceding pages 
that little need be said here about it. From it has come a very large part of the 
fauna, not only of the Murray Islands and Barrier Reef, but of the coast of tropical 
Queensland as well. It is impossible to say just how many Australian species or 
their ancestors reached the continent by this route, but careful examination of 
the ‘“Tabulated List”’ (p. 192) suggests that more than 125 of the 210 or more 
Barrier Reef and Queensland echinoderms may have done so, and almost certainly 
not fewer than 80 did. It does not seem necessary to offer here a list of these, 
‘Tf this prove to be the young of C. rotalaria, it will not seriously affect the propriety of placing it here, for it 
is highly probable that C. rotalaria is one of the original Australian species which have extended their range through 
Torres Strait. 
