HOUTMAN’S ABROLHOS. 151 
Pseudoceros. One of the most noteworthy features of this grand Doris was its 
remarkably brilliant colour. This differed somewhat among individual specimens 
observed. Red was always the predominating hue, but this varied from a dull orange 
or Indian red in some examples to the most brilliant vermilion tint characteristic 
of the specimen figured. This gorgeous tinting of the general surface of the body 
is, by contrast, considerably enhanced by the elegant scarlet and white frill-like 
border which encompasses the entire periphery. Such was the abnormal size and 
brilliancy of the first example of this Nudibranch that fell under the writer’s 
observation, floating in the water at a little distance from the Rat, Island jetty, 
that the possibility of its being a living organism did not immediately present 
itself. It was, in fact, passed by at first sight, under the impression that it was 
simply a portion of the lung of a freshly-killed sheep that had been immolated 
that morning for the use of the station. When it was seen a second time, it had drifted 
nearer to the jetty, and the recognition of the splendid prize awaiting appropriation 
dawned upon one’s vision as a revelation. With reference to its magnificent pro- 
portions and brilliant hue, the writer has provisionally conferred upon this fine 
Nudibranch the regal title of Doris imperialis. 
To conclude with a consideration of the most salient facts chronicled in this 
Chapter—namely, the very remarkable interblending of both tropical and temperate 
marine organisms, and more especially the phenomenon of species occurring in the 
Houtman’s Abrolhos which, while indigenous to Torres Straits and the north 
Queensland coast, are not inhabitants of the adjacent sea-board of Western Australia— 
but one interpretation appears to be permissible. This is that an ocean current 
setting in from the equatorial area of the Indian Ocean penetrates as far south as 
this island group without impinging on the adjacent mainland, and that that stream 
is the medium that has conveyed thither the floating germs of the Ccelenterates 
and Holothuride, which possess such essentially tropical affinities. The presence - 
here of migratory tropical fishes admits also of the explanation that they would 
very naturally follow a warm stream bringing them to such congenial conditions and 
environments as exist in and among the Houtman’s Abrolhos. That this interpret- 
ation is the correct one is substantially supported by a reference to the Admiralty 
Charts denoting the courses of the ocean currents in this region, that-have been kindly 
placed at the writer’s disposal by the Hydrographic Department of the Admiralty. 
In one of these, No. 2640, there is, in fact, clearly indicated a prevailing northerly 
drift of the ocean currents along the Western Coast of Australia, but at the same 
