144 SEAWEEDS 



been placed in this group by Mr. Carruthers. It 

 possesses stalks more than a foot in circumference, 

 and must have been a colossal member of the group. 

 Its filaments are entirely free from cross-walls, and 

 are bound together by very fine lateral branches, 

 though these do not appear to terminate in haptera, 

 but rather wind round the larger main filaments. 



The Reproductive Organs are known only in the 

 genus Halimeda, and are zoosporangia producing 

 biciliated zoospores. The zoosporangia arise from 

 the margins of the flat fronds, and are round or 

 pear-shaped bodies borne on branching filaments. 

 They are green in colour and not separated by 

 cross-walls from the filaments of the thallus. The 

 zoospores are very small and green in the posterior 

 part, hyaline at the ciliated end. They are pro- 

 duced in great numbers. No observation has been 

 made of their possible conjugation or germination. 



The genus Codiophyllum, placed here doubtfully 

 by Wille, is identical with a red seaweed Tham- 

 noclonium. 



The Geographical Distribution. The order is 

 almost wholly tropical, though Penicillus, Udotea, and 

 Halimeda have each one representative in the 

 Mediterranean. All the genera except Callipsygma- 

 (of somewhat doubtful validity) are represented in 

 the West Indies, while Avrainvillea, Halimeda, and 

 Udotea are abundant also in the warm Indian Ocean, 

 Malay Archipelago, and Pacific islands. Penicillus 

 has not quite such a wide range, but occurs in the 

 West Indies, Australia, and Moluccas. Callipsygma 

 is known only from Australia. 



