F. Børgesen: General remarks. 493 



and Hervey's newly published work on the algal flora of these 

 islands. 



Of the remaining 166 West Indian species, 112 species are 

 also found in the Mediterranean and at the warmer Atlantic coasts 

 of Europe and Africa and 111 are likewise found in the Indo- 

 Pacific ocean. Practically speaking the same number of species 

 is therefore common to both of the areas in question, and the West 

 Indian algal flora may therefore be said to be equally related to 

 both the different areas. If we look at the Chlorophyceæ alone we 

 shall meanwhile find that they occupy a somewhat different 

 position; of this group 90 species are found at the islands and of 

 these species 46, that is more than the half, are common to the 

 Indo-Pacific, while only 35 are found both in the West Indies 

 and in the Mediterranean and adjacent region of the Atlantic. 

 With regard to the Phæophijceæ the corresponding numbers are 

 18 and 14. On the other hand the West Indian representives of 

 the Rhodophijceæ are more closely related to the Mediterranean- 

 Atlantic flora (63 species common to both) than to the Indo- 

 Pacific ocean (only 47 species in common). 



From the above we have seen that the West Indian algal 

 flora does resemble in an almost equal degree the flora of the 

 Indo-Pacific ocean and that of the Mediterranean Sea and adja- 

 cent warm parts of the European and African Atlantic coasts — 

 in the case of the Chlorophyceæ the resemblance being even far 

 greater — and that in spite of the fact that the two areas are 

 apparently so distinctly separated. 



Murray was the first to point out this striking similarity. 

 In his paper; "A comparison of the marine floras of the warm 

 Atlantic, Indian Ocean, and the Cape of Good Hope"\) he has 

 compared these areas thoroughly. As to those of the Indo-Pacific 

 ocean and the West Indian he writes: "We have here two 

 tropical marine floras cut off from each other by a permanent 

 continental area, and communicating only via the Cape". And 

 he tries to explain in the following way how this great similarity 

 has arisen: "That these floras have been periodically mingled at 

 the epochs of warmer chmate at the Cape seems a reasonable con- 

 clusion with regard to a group of such antiquity as the Algæ". 

 That some species by passing the Cape may have been able to 

 1) In Phycological Memoirs edited by George Murray, Part II, 1893. 



