108 CEYLON MARINE BIOLOGICAL REPORTS. 



liypothesis of a connection by way of the Cape. Thus there are several Caulerpa species which tlie West 

 Indies and the Pacific-Indian Ocean have in common tliat do not occur fartlier west than Ceylon 

 and the peninsula of India. Such are G. verticillata, taxifolia, and cupressoides , and to these could also 

 be added one species wliich is only known from the West Indies and the Pacific, but not from the Indian 

 Ocean, viz., 0. fastigiata. These species have, therefore, a distribution which in the West does not 

 reach the east coast of iVfrica, but have, on the other hand, a more eastern centre of distribution in the 

 Pacific. To suppose that these species too, could possibly have come by way of the Cape to reach the 

 West Indies, or vice versa, seems unreasonable, for in that case they could scarcely have failed to leave 

 traces in i.\fiica, whereas their distribution is very naturally explained by the supposition of a connec- 

 tion between the Atlantic and Pacific across Central America. 



I therefore consider it much more probable that the explanation of the resemblances pointed 

 out by MuREAY between the algae of the West Indies and those of the Indian Pacific Oceans, must 

 bii looked for rather in the historical development of the connection of land between North and South 

 .Vmerica, which shows that the whole Carribean Sea was once only a bay of the Pacific, than in the 

 assumption that it depends on a connection via the Cape in a time when the external conditions for 

 tropical algae were more favourable there than to-day. 



For a definitive proof of the above a more detailed comparative investigation of the whole algal 

 vegetation must, of course, be undertaken, and I hope to be able to return to this matter before long. 



For the present I will content myself with pointing out that the geographical distribution f)f 

 Caulerpa as well as that of the marine phanerogams, clearly indicates that the relation of the marine 

 tlora of the West Indies to that of the Pacific-Indian Ocean must not be determined without taking 

 nito consideration the geological history of the connecting fink of land between the two Americas. 



VI.— LIST OF THE SPECIES. 



I.— CAULERPA VERTICILLATA, J. G. Agardh. 



J. G. Agardh, Till Algernes Systematik, I., p. 6. 



A. Weber v. Bosse, Monographic des Caulerpes, p. 267. 



Syn. Stephanocoelium verticillatum, KUtz. 



Murray, Catalogue of Ceylon Algae in the Herbarium of the British Museum, p. 38. 

 Exsicc: WiTTROCK et Nordstedt, Algae exsiccatae. No. 347 ! 

 Ferguson, Ceylon Algae, No. 233 and 425! 



This plant occurs at Galle in a small but clearly defined district where it constitutes almost the 

 whole of the vegetation. It grows at Galle exclusively around the mouth of the stream or canal that 

 enters the sea at Victoria Park to the north of the town proper. The low rocks, which are here quite covered 

 by sand and mud formed by the stream are entirely coated with C. verticillata together with a Uttle 

 Ceramiaceoe, and these form the bulk of the vegetation. However, O. verticillata did not grow higher than 

 up to the low-water mark, so that it was never exposed at low-water. 



Structure of the shoots. — As Professor Reinke in his work on Caulerpa (page 7), in describing this 

 species, confesses that he has been unable to confirm the statement to be found in the literature of the 

 subject, viz., that it has a horiz(mtal rhizome, we may here briefly describe the structure of its shoots 

 and its manner of growth (fig. 1). 



It always grows in tliick tufts, surrounded by sand, out of which the green tufts stick up so 

 nigh that they are fully exposed and wave to and fro in the swell. If we examine such a vertical 

 assimilating branch, we shall find that it is rather richly ramified below the sand, and consists of up 



