TRANSACTIONS OK SECTION D. 733 



notwithstanding; tlie fact that it lay some two degrees south of Shark's Bay, the 

 character and composition of the coral reefs proved to be entirely distinct. In 

 place of the extra-tropical Turbinarife the corals of the Abrolhos Reefs comprise, 

 as in essentially tropical districts, numerous varieties of branching Madreporae, 

 or so-called Stag's-horn corals, commingled with many species of Porites, Monti- 

 pora, Pocillopora, Seriatopora, Coeloria, Mussa, and other intra-tropical reef-build- 

 ing species. 



A yet more remarkable phenomenon, however, is recorded by Mr. Saville-Kent 

 in connection with the marine fauna of Houtman's Abrolhos. This is the circum- 

 stance that he discovered on its reefs three of the most valuable economic species 

 of Holothuridre or Beche-de-mer, identical with types that are systematically 

 collected in Torres Straits, and throughout the northern moiety of the Queensland 

 Great Barrier Reef, but which are unknown to the coastal reefs of Western 

 Australia further north, and where their place is taken by a distinct and much less 

 valuable commercial species. 



The fish fauna of Houtman's Abrolhos, while corresponding to a large extent 

 with that of the temperate Australian seaboard, as instanced by such genera as 

 Pagrus, Aulopus, and Seriola, is also associated with many essentially tropical 

 species, including, notably, a large assemblage of brilliantly coloured Labridae, or 

 Parrot-fishes. Certain of these Labridre, while not obtained by Mr. Saville-Kent 

 in collections made among the mainland reefs of Western Australia, were familiar 

 to him, as in the case of the Holotlinridre, as denizens of Torres Straits and the 

 northern region of the Great Barrier Reef. 



The anomalous character of the marine fauna of Houtman's Abrolhos as 

 herein deBned can only be accounted for by the assumption that an ocean 

 current setting in from the equatorial area of the Indian Ocean penetrates as far 

 south as this island group, and has borne with it the floating embryos of the 

 Holothuvidfe and Ccelenterates, &c., that so characteristically distinguish it. A 

 reference to the Admiralty charts, dealing with the ocean currents of this region, 

 supports this interpretation to a considerable extent ; indicating, as a matter of 

 fact, a prevailing northerly set along the western coast of Australia, but at the 

 same time a distinct southerly intrusion of the waters of th? Indian Ocean at some 

 distance off shore down towards and closely approaching Houtman's Abrolhos. 

 In further support of this interpretation Mr. Saville-Kent also determined by 

 synchronous readings of the thei-mometer at the coldest season of the year, July, 

 that as great a diiference as from ten to fourteen degrees Fahrenheit distinguished 

 the surface temperature of the sea at respectively the Abrolhos Islands and in 

 Champion Bay. Mr. Saville-Kent remarks, in conclusion, that much scope is yet 

 left for further investigation in this direction ; while with respect to the anomalous 

 character of the marine fauna it would be greatly to the advantage of marine 

 biological science if a thoroughly exhaustive investigation thereof could be 

 carried out. 



9. On Hereditary Polydactylism. By Dr. Gregg Wilson. 



10. On the Rejyj-oduction of the Common Crab. By Dr. Gregg Wilson. 



TUESDAY, SEPTEMBER 17. 

 The following Papers were read : — 



1. Ohservations on Instinct in Young Birds. 

 By Professor Lloyd Morgan, F.G.S., Assoc. R.S.M. 



This paper dealt with observations on young moorhens, chicks, martins, and 

 swallows with a view to determine how far the activities involved in locomotion 



