144 SEA WEEDS 
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- 
nocloniwm. 
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. 
