CR51 



■« &-rat Sri tail 



"tJA* >ofa*-.:cl J»Bfc:aoLi; DL-Aj-pi I _«>d» 



Fig. 227 Geographical distribution of Chamaedoris and Clado- 



cephalus. (After Svedelius.) 



satisfactory explanation is the existence of a former sea passage 

 across the Suez isthmus.^ In the flora of the northern part of the 

 Arabian Sea, out of a total of 137 species and varieties, 22 per cent 

 are endemic, 52 per cent are Indo-Pacific and 59-6 per cent also 

 occur in the Mediterranean and Atlantic Ocean, the most striking 

 example being Cystoclonium purpureum which does not now exist 

 between its widely separated stations along the southern shores of 

 France and in the Northern portion of the Arabian Sea. In the case 

 of the Indo-Pacific species of the Arabian Sea, it is often found that 

 they are absent from the intervening tropical waters, so that their 

 distribution must be explained as occurring at a period when the 

 tropical waters had a more equable temperature. 



1 Species, e.g. Caulerpa racemosa, Soliera dura, are known from the eastern 

 Mediterranean, which have migrated from the Indian Ocean. 



431 



