THE CEYLON SPECIES OP CAULERPA. 107 



Pacific, and the distribution of C. manatorum coincides with that of Th. testudinum, i.e. is exclusively 

 confined to the West Indies. 



Similar is the distribution oi the two Halodule sipecies, viz., H.uninervis (Forsk.) Aschers., inthe 

 Indian Pacific Ocean and H. Wrightii Aschers., in the West Indies. The latter seems to occur also on 

 the west coast of Africa, but not in the south at the Cape. These species are so similar to each other 

 that OsTENFELD ("Flora of Koh Chang," Part V., Hydi-ooharitacese,Lemnaceae, &c., page 262) ," who has 

 devoted a comparative study to them, says : " On the whole it is not possible to distinguish the two species 

 when sterile, except using their quite different geographical distribution as criterion." 



Also within the genus Halophila analogous distribution can be traced. The majority of the 

 Halophila species are at home in the Red Sea, Indian Ocean (they do not reach the Cape, however), 

 and the Pacific, and, besides, there occur very closely allied forms in the West Indies, but not from other 

 parts of the Atlantic coasts of South America, nor from the west coast of Africa. Ostenfeld has 

 lately described from the Gulf of Siam (Koh Kahdat) a H. decipiens which is so strikingly Hke the 

 West Indian H. Baillonis that he says {loc. cit., p. 261) : "If the geographical distribution was not so 

 quite different I should prefer to regard it as a variety of H. Baillonis, but it is not probable to 

 suppose such a connection, as the sea phanerogams generally have very natural and limited areas and 

 H. Baillonis is confined to the shores of the West Indian Archipelago." 



Ergo : numerous marine species with wide distribution in the Indian and Pacific Oceans, and which 

 are lacking on the east coast of Africa and at the Cape, find their parallel within the West Indies in often 

 closely allied species which are exclusively confined to the West Indies. The marine flora of the West 

 Indies, at least the marine phanerogams and Caulerpa, thus show much greater resemblance and affinities 

 to the Pacific and Indian Oceans than to the rest of the Atlantic. That this is the case also with regard 

 to other groups of algae is certain, and I hope to return to this point again. 



That the same is the case also within certain groups of the faima, where relationship is 

 traceable between West Indian and Pacific species, has been pointed out by several investigators 

 (Wallace). 



One is therefore forced to the opinion that the marine flora and fauna of the West Indies, in part 

 at least, is an off-shoot of the Pacific. In the earlier epochs of the Tertiary Age, and at least up to the 

 beginning of the IVIiocene period. North and South America, as just mentioned, were separated from 

 each other so that the Carribean Sea was only a bay of the Pacific, or a kind of straits between the Pacific 

 and the Atlantic, and not before the transition of the Tertiary Age into the Quaternary Age did the volcanic 

 formations arise which make up the present Isthmus of Panama and which ever since have separated 

 the Atlantic from the Pacific. But since the Carribean Sea was at relatively so late a period no more than 

 a bay of the great unbroken ocean which is formed by the Indian Ocean and the Pacific, what is then more 

 natural than that this part of the Atlantic should stiU often show resemblances to the Pacific more than 

 to the rest of the Atlantic. And that such a primitive and old group of plants as Caulerpa already 

 then had species that stiU survive, is highly probable ; since other tertiary organisms are, as far as their 

 species go, very closely aUied to or the same as stiU existing species. And that also such a primitive group 

 as the sea phanegorams in the West Indies and in the Pacific and Indian Oceans should be represented 

 by species that are very closely aUied, if not quite identical, follows then as a matter of course. That 

 the species are not quite identical, perhaps only shows that they, after being isolated, have undergone 

 somewhat different evolution, which however has not led them very far apart. This is best shown by 

 this, that among the species in common there are no less than two genera [Thalassia, Halodule) and 

 one very characteristic sub-genus {Phycoschcenus of Cymodocea), all of which consist of only two species, 

 of which one is exclusively confined to the West Indies, the other to the Indian-Pacific Ocean. 



By assuming that the similarities between the algal florae of the West Indies and Pacific and 

 Indian Oceans depend on a former direct connection across the present American belt of land, a number 

 of peculiarities in the distribution of some algae can be explained which cannot be explained by the 



