HOUTMAN ABROLHOS ISLANDS. 143 



Abrolhos Islands, but Micliaolsen adds a note concerning them in a report *, 

 apparently as a result of an examination of collections in the West Australian 

 Museum. His report is somewhat singular for he makes no reference to the 

 only marine biologist who had visited the islands, and adds: "An exact 

 description of these islets and of their physiographic faunal relations has 

 been given by Helms. After studying the zoological materials of the 

 Abrolhos in the West Australian Museum in Perth, I can affirm Helms' 

 assertion about the marine fauna of the Abrolhos.''' Now, the first mention 

 of the tropical character of the marine fauna of the Abrolhos is due to 

 Saville Kent. Helms states that this naturalist visited the islands but does 

 not refer to his paper, and indeed does not enter into any discussion on the 

 character of the marine fauna or on the southern position of these islands. 

 Yet Michaelsen states that he can support the remarks of Helms on the 

 character of the marine fauna, and then goes on to account for the tropical 

 character of this fauna. His explanation includes an exactly similar theory 

 to that propounded ten years before by Kent. This is put forward without 

 even the temperature records that Kent had made, and without reference to 

 Admiralty Charts for confirmation. We must consider in some detail the 

 further remarks of Michaelsen to the effect that a " Kalter Auftrieb " rising 

 from the depths of the sea may also explain the difference between the 

 marine fauna of the Abrolhos and the coast. 



The term " Kalter Auftrieb " is used by the German hydrographers to 

 denote the rising cold waters which are met with along a lee shore, and are 

 due to the removal of the more superficial waters to windward. This 

 phenomenon accounts very well in many [daces for a great difference in 

 temperature between the coastal waters and those some little distance out, and 

 excellent examples are to be met with in the Baltic Sea and the Sea of Azof, 

 as well as along the coasts of some continents when strong offshore winds 

 are blowing. This vertically moving colder water is also held to account for 

 the lower sea temperatures in the Atlantic and Pacific Oceans along the 

 Western coasts of Africa and South America in the region of the trade winds, 

 one of the results of which is the well-known absence of coral reefs along the 

 West coasts of these continents. 



If, however, we examine the following diagram (text-fig. 4), which shows 

 the position of certain isotherms between the land masses of Australia, South 

 America, and South Africa, we shall see that there is a difference between the 

 west coast of Australia and that of these other two continents. 



" The inflowing and outflowing waters probably find their way not only 

 through the wide and deep channels between fhe islets, but to some extent 

 through the body of the reef, which in its upper portions would appear to be 

 almost as open and pervious as a sponge." — Judd. " Materials sent from 



* "Die Tierwelt Sudwest-Australiens unci ihre geograplrische Bericlitegen."' Mitteil. 

 Qeog. Ges. Hamburg, Bel. xxii. 



LINN. JOURN. — ZOOLOGY, VOL. XXXIV. 11 



