127 



the kindness of Prof. R. J. Harvky Gibson we have had the privilege of examining- a specimen 

 from the type-locality. 



The main characteristic of U. argentea lies in the position and form of the lateral 

 appendages, which are close together, short and of approximately equal length, having either 

 a simple and inflated (figs. 61, 62), or a lobed (figs. 58 — 60), head. The proximity of the 

 branchlets causes the heads to be appressed against each other above and thus to form a 

 closed pseudo-cortex covering the main filaments. 



The lateral appendages of the frond-filaments of U. argentea exhibit sufficiënt varia- 

 bility in different specimens to suggest a separation of the plants into two groups. The typical 

 form is found in the Red Sea and the Indian Ocean (fig. 57), and as far east as the coast 

 of Oueensland. lts lateral appendages bear each a distinctly and variously lobed capitulum, 

 which is inflated and adorned with a few low bosses, as in specimens from Cargados (see 

 figs. 58 «, 58 c and 59) and Oueensland; or complanately flattened and subpalmately lobed as 

 in the Lirung specimens, (see figs. 58^ and 60). The Karkaralong specimens of the Siboga 

 Expedition bear appendages of both these kinds, and also here and there show groups of 

 appendages almost as simple as those of var. sptimosa (see fig. 22 e). 



The var. spumosa (fig. 15) occurs only in the eastern Indian Ocean and is distinguished 

 from the type by the simple elongate pyriform capitulum (figs. 61, 62), which terminates each 

 of its lateral appendages. The surface of the frond is minutely spumose or polyporoid ; but 

 this character is also shared by some of the plants of f. typica. 



The nearest ally of U. argentea is U. occidenta/is, a species confined to the West 

 Indies and distinguished by its narrower frond-filaments with shorter lateral appendages (not 

 or rarely exceeding 100 u. in length), the capitula of which are more divided and are adorned 

 with more numerous and smaller prominences. 



Inasmuch as the branchlets in U. argentea abut against one another and are not intricated, 

 they are easily teased apart after decalcification, and are thus in marked contrast to the lateral 

 appendages of U. flabellwn, which are so much interlocked that it is almost impossible to 

 separate them without tearing them. 



U. argentea occurs in the Indian and Pacific Oceans. 



12. Udotea oecidentalis n. sp. 



Syn. Udotea Halimeda Dickie in Journ. Linn. Soc. (Bot.) XIV. 1875 p. 312. 



Udotea flabcllata Murray in Journ. of Bot. XXVII. 1889. p. 238 (pro parte). 



Udotea Halimeda Murray op. cit. p. 239. 



Udotea argentea Howe in Buil. Torrey Bot. Club. XXXVI. 1909. p. 99. 



Udotea argentea Collins Green Alg. N. Amer. in Tufts College Studies II. 1909. p. 396. 



Hab. Atlanic. West Indies, St. Thomas, 5 — 15 fathoms, " Challenger" Expedition, (sub. nom. 

 " U. Halimeda") in Herb. Mus. Brit.! — St. Jan, F. Bórgeseit, herb. n os 1767, 2101, and an 

 unnumbered specimen! — West Indies, Fleming in Herb. Mus. Brit.! 



Plants up to 8 cm. high, much calcified. Root-mass small, bulbous, fibrous. Stipes simple, 

 terete, short (up to 1 cm. long), slender (1.5 mm. thick). 



