President's Address. vn 



known to visit Mossel Bay. There is no record of its having ever 

 been seen at Algoa Bay, and it is quite unknown on the east coast. 

 Its distribution is therefore intimately associated with the colder 

 waters of the west coast. It is indeed probable that some light 

 might be thrown on its relative abundance or scarcity at different 

 periods by a more intimate knowledge of the temperature conditions 

 prevailing in different years. Another example, from the group of the 

 Crustacea, illustrates perhaps even more forcibly than the last two 

 the effect of the changing environment we meet in passing round 

 the South African coast ; this is the large Crawfish (Palinurus 

 lalandii). This Crustacean occurs in such quantities in Table 

 Bay that the supply was sufficient to keep a large canning 

 factory going. The supply seems practically inexhaustible. It is 

 found in the same abundance northwards beyond Angra Pequena. 

 It occurs also in quantity in Hout Bay, but not commonly in 

 False Bay. The samples I have seen from this region are much 

 smaller in size, and the same is to be said of those procured 

 further east, at Hermanus. They are undoubtedly the same 

 species, but smaller. There is yet no record of their occurrence 

 to the east of this locality, and a different species has been found 

 at Mossel Bay, this also in its turn seems to be absent from the 

 Natal coast, where still another and much smaller species is found, 

 and where also the Crustacean fauna shows a considerable increase 

 in species as compared with that of the west and south coasts. 



Such instances could be easily multiplied, but these are sufficient 

 to indicate the general tendency. One other example, however, 

 may be mentioned as illustrating the same feature in a reverse 

 way, viz., the pearl oyster Avicula. Its first definite appearance 

 is on the south coast, just beyond Cape Agulhas. Specimens 

 hitherto found, however, have been so small as to be of little 

 commercial importance. It seems to occur all along the south 

 coast from this point. It is found on the east coast as far as 

 the Mozambique Channel, where it is larger and more abundant. 



We see, therefore, that the different physical conditions on the 

 east and west coasts are reflected in the character of the fauna, 

 the general rule seeming to be that in the colder waters the 

 species are fewer, the individuals more numerous, while the 

 warm waters are characterised by greater variety of species and 

 fewer individuals of any one species. In some of the cases cited 

 the cold-water forms grow to a much larger size than in others the 

 warm-water forms. 



Having noted the variety in the fauna as illustrated by a few 

 species, we naturally look about for some explanation. It might 



