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 ciliata ; 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, Labridee and Scaride. 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 Holothuride, 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 pelagicus, 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 
