Ptimu^ " drtvl BritV't 



■ lAJt JohM-.or. 1 ;wa*i:3n _;; £±.-.bv.-fll. 



Fig. 226 Geographical distribution of species of Neomeris. After 



Svedelius.) 



Cladocephalus (cf. Fig. 227). Although there is at present no very 

 adequate explanation for this distribution, three possible hypo- 

 theses may be suggested, but there does not appear to be any evi- 

 dence which supports one of them more than the others : 



(a) Migration via the Cape. 



(b) Migration via the Pacific and Panama, the related species 

 perhaps still existing in the Pacific but not yet recorded. 



{c) The related species or representatives in the interzone have 



died. 

 (3) There are some genera which are common to the Mediter- 

 ranean and the Indo-Pacific region, e.g. Codium bursa group, the 

 vicarious pair Halimeda tuna in the Mediterranean and H. cuneata 

 in the Indo-Pacific, Acetabularia mediterranea and other species of 

 Acetabularia in the Indo-Pacific (cf. Fig. 228). In this case the only 



430 



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