150 THE NATURALIST IN AUSTRALIA. 



The fish fauna of Houtman's Abrolhos was found, as might be anticipated in 

 virtue of its essentially migratory constituents and its proximity to areas of relatively 

 cool water, an interesting intermixture of both tropical and temperate species. 

 Conspicuous among the fishes indigenous to the temperate Australian sea-board may 

 be mentioned such species as the Snapper, Pagrus major ; the Sergeant Baker, Aulopus 

 purpurissatus ; Australian Whiting, Sillago ciliala ; Yellow-tail, Seriola gigas ; and a species 

 of what in the Sydney market would be designated a Morwong, Chilodactylus. Charac- 

 teristic tropical fish were, on the other hand, specially represented by innumerable varieties 

 of Parrot-fishes, Labridse and Scaridse. Many of these, it is interesting to observe, such 

 as species of Julis and Pseudoscarus, had not been met with by the writer further north 

 on the Western Australian coast, but were familiar to him, as in the case of 

 the Holothuridae, as inhabitants of Torres Straits and the Queensland Great Barrier 

 region. Such species, again, as Platax orbicularis and Mesoprion Johni, the Golden 

 Snapper of Thursday Island, Torres Straits, may be mentioned among the essentially 

 tropical forms that were found frequenting the Abrolhos reefs. 



No zoological groups in addition to the foregoing yielded such substantial 

 evidence of tropical affinities, though the investigations prosecuted were necessarily 

 of too short duration to allow of any very positive deductions in this direction. 

 Among the Crustacean Class Crawfish, Palinuri, were exceedingly abundant and 

 identical with the ordinary Perth and Fremantle market type. Crabs referable to 

 genus Grapsus, also similar to those frequenting Fremantle harbour, swarmed at the 

 bases of the more sheltered coral limestone cliffs. There was missing, however, from 

 this locality the toothsome Blue Crab, Neptunus pelagicm, that abounds along the 

 Western Australian coast from Shark's Bay southwards. It was here replaced 

 by another smaller and more essentially tropical representative of the same genus. 



Apart from considerations of tropical or temperate affinities, reference may 

 be here made to a most magnificent Nudibranchiate Mollusc obtained by the author 

 in the neighbourhood of Rat Island, in the Eastern Group of the Abrolhos. The 

 species, of which a coloured illustration is reproduced in Chromo-Plate V., is, as shown 

 by the conformation of its gills or branchial plume, referable to the genus Doris, 

 of which it represents a new and, so far* as ascertainable, the largest discovered 

 species. In its condition of full extension, as delineated in the illustration, it 

 occupies a quadrangular area of no less than nine or ten inches long with an 

 inch or two shorter diameter, but it is at the same time of so flattened a shape 

 as to more closely resemble a huge complanate Planarian akin to the genus 



