264 TAYLOR 



to the total better known species of individual algal classes, not the whole 

 flora. This really expresses the proportions of the important species and 

 their range trends. The group of species which occurs in the Caribbean 

 but ranges to the northward is hardly more than a third as large as any 

 of the others. The strictly Caribbean contingent is about as large as the 

 Caribbean and southern, or the widespread group (which will include 

 the most cosmopolitan species). Specifically, applying the principle of 

 comparing the distribution ranges of better known species, we find by 

 Table 2 that only 11.0 per cent of the species extend beyond Florida into 

 the Carolinas, hardly a thousand kilometers from the rich tropical flora 

 of the Florida Keys. Remember that we are considering a relatively well- 

 explored region. By contrast, the southern extension of the flora to Brazil 

 involves three times as many, or over 33 per cent of the species, and the 

 best known parts of the coast of Brazil are in the vicinity of Rio de 

 Janeiro, over 5000 kilometers away from the Caribbean. In fact, the 

 group which has an extended southern range is larger than the ubiquitous 

 group of algae, many cosmopolitan, which range both north and south, 

 and which constitute about 27.5 per cent of the Caribbean flora. It is 

 also larger than the strictly Caribbean fraction, which is about 27.9 per 

 cent. If we go into more detail and examine the individual algal classes, 

 we find that the smallest, the Phaeophyceae, is the most extreme in these 

 respects, for only 5.7 per cent of the Caribbean species range northward 

 while nearly eight times as many, or 47.2 per cent, range southward, as 

 against less than three times as many in either Chlorophyceae or 

 Rhodophyceae. 



Many examples of species with distinctive ranges on the American 

 coasts could have been provided from each of the groups of larger marine 

 algae, but two examples of each range type are a sufficient sample. Of 

 those which range widely from the Caribbean both northward and south- 

 ward along the American coast, we select from the Chlorophyceae Uha 

 lactuca, known from the Magellan Strait to the subarctic waters of New- 

 foundland and nearly cosmopolitan. The map of Fig. 1 shows the avail- 

 able records. Reports in the literature of this species are particularly 

 suspect, but the occurrences in our range seem well substantiated. For 

 comparison note Sargassum filipendula, shown in the map of Fig. 2. This 

 is not a cosmopolitan species, though it ranges widely on the eastern 

 American coasts, being quite distinct in its northern range but less easily 

 delimited when one has southern collections. It reaches to south-central 

 Brazil. 



More restrictively, we may consider two species which, while wide- 

 spread in the Caribbean, seem only to range northward. One, Aegira 



