57 



3. Rhipilia orientalis n. sp. 



Hab. INDIC. Siboga Expedition. Stat. 81. Pulu Sebangkatan, Borneo Bank, 34 m. Coral bottom and 

 Lithothamnion. n° 334! — Stat. 149. Lagune of Fau Island, reef! 



Plants brownish-green, small, gregarious, stipitate ; stipes up to 1 cm. long, 0.1 — 0.2 cm. 

 thick, expanding above into the frond. Frond small, mostly 1 — 3 cm. long, r — 2.5 (rarely 4) 

 cm. wide, varying in shape from infundibuliformly and excentrically peltate to cuneately or 

 rotundately flabellate, very thin, translucent, almost like brown-stained muslin, not or rarely 

 zonate, margin fimbriate or lacerate. Frond filaments (spirit-specimens) 30 — 50 ij. in diam., very 

 laxly interwoven; pseudo-lateral branchlets long, varying from 70 to 350 p., usually about 1 70 ƒ/, 

 frequent but not abundant; true lateral branchlets rare or absent. [Figs. 134 — 136]. 



Until the present time, Rhipilia has never been known to occur in the Eastern hemisphere. 

 But, among the algae collected by Madame Weber van Bosse during the Siboga Expedition, 

 are several specimens of what proves to be a new species of Rhipilia. It was collected both 

 on muddy reefs at tide level and also at a depth of 19 fathoms on Borneo Bank; but the two 

 sets of plants show no difference in habit or structure to correspond with this difference in depth. 



The plants are brownish, small and have a very thin frond almost like coarse muslin 

 in texture, varying in form, like R. tenacitlosa, from rotundate-flabellate to excentrically peltate. 

 They are rarely zonate and have a very loose fimbriate margin. When dry and adhering to 

 paper, they sometimes look like a mere smudge (fig. 134). 



From both the preceding species R. orientalis differs in its brown colour, small size, the 

 exceeding thinness and very loose texture of its frond, and the greater average length of its 

 pseudo-lateral branchlets (figs. 135, 136). From R. tomentosa it also differs in often having an 

 excentrically peltate frond with stipes shorter and thinner, and frond filaments more slender. 

 From R. tenacitlosa it also differs in having pseudo-lateral, rarely lateral, branchlets of very 

 much greater lengrth. 



6. Cladocephalus M. A. Howe, emended. 

 (Figs. 32—35; i37—i4o)- 



This genus was founded by Dr. Howe, in Buil. Torrey Bot. Club XXXII. 1905 p. 569, 

 on a new alga C. scoparius, collected by him in shallow water in a tidal pond at Georgetown, 

 Great Exuma, Bahamas. The distinguishing character of Cladocephalus is the intricate labyrin- 

 thiform nature of the cortex, which is composed of repeatedly divaricato-dichotomous filaments 

 closely interwoven. The author describes it thus (loc. cit. p. 570): "The cortex is formed by 

 "branches originating subdichotomously from the more peripheral members of the medullary 

 "strand and becoming afterwards apparently lateral. These branches then undergo repeated 

 "divaricate forkings with a gradual diminution of diameter until finally they may have only 

 "one-fifth or even one-twelfth the diameter of the filaments of the central strand". 



As we have shown in a paper describing the Indian Ocean Algae of Mr. J. Stanley 

 Gardiner (in Trans. Linn. Soc. (Bot.) ser. 2, vol. VII. 1908, p. 177, and loc. cit. (Zool.) XII. 



SIBOGA-EXPEDtTIK LXII. S 



