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 Holothuridte, 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 



