180 SLADEN TRUST EXPEDITION TO ABROLHOS ISLANDS. 



latitude (the Abrolhos are probably the most southern coral islands in the 

 world), and the fauna of this region of the southern Indian Ocean. 



2. There is evidence that the temperature of the sea at the Abrolhos is 

 usually some degrees higher than at the adjacent coast, and that as a result 

 the temperature during the winter months rarely falls below 20° 0. 



if. In consequence of this hydrographical condition, the temperature of 

 the water at the Abrolhos only very exceptionally falls below a point that is 

 detrimental to the active growth of reef-building corals. 



4. The difference in temperature between the coastal waters and those 

 50 miles out, is due to a tropical current from the North and North-East, which 

 passes down the coast but is deflected away from it, leaving a strip of colder 

 water against the land. 



5. Any phenomenal preponderance of tropical species in the marine fauna 

 of the Abrolhos region of the Indian Ocean is due to this tropical current. It 

 remains to be seen, when the collections are worked up, to what extent the 

 marine fauna is a mixture of Tropical and Southern types*. 



6. A great blank in our knowledge of the distribution of marine organisms 

 in the southern Indian Ocean will be filled up by the study of these collections 

 from the Abrolhos region in conjunction with those to be obtained from an 

 expedition to the north-western coast of Australia, which is to follow as part 

 of this investigation. 



The collections so far examined give every indication of this, as for 

 example the record of a new Enteropneust, and many species of other 

 groups for the first time on the West Australian coast. 



EXPLANATION OF THE PLATES. 



Plate 10. 

 [Fig-. 1.] Face of Limestone cliff, Turtle Bay, East Wallaby Island. 



Plate 11. 



[Fig. 2.] Lesser Noddy, on nest in Mangrove Swamp. 



Plate 12. 

 [Fig. 3.] Noddy Terns nesting on Pat Island. 



Plate 13. 

 Fig. 4. North-eastern coast of East Wallaby Island. 

 Fig. o. Limestone cliffs, Turtle Bay, East Wallaby Island. 



Plate 14. 

 Fig. 6. Undercut Limestone, North Island. 

 Fig. 7. Limestone "Pinnacle" on reef-flat, West Wallaby Island. 



* The fishes, at least, appear to be chiefly Southern forms. 



