THE GREEN AI.GAE OP NORTH AMERICA 91 



to a diameter of 10 cm. or more. Dredged in about 40 meters, 

 Virgin Islands, Borgesen. 



The horizontally expanded filaments of the head seem to be 

 an adaptation to its deep water habitat ; otherwise it is of the 

 typical form. 



Page 394 and p. 102 of supplement, for Key to the Species of 

 Udotea, substitute, 



i. Whole flabellum with a stony coating. 2. 



i. No general stony coating. 3. 



2. Branches forming the cortex of the flabellum capitate. 



6. U. occidentalis. 



2. Cortical filaments not capitate. 5. U. Flabellum. 



3. Flabellum with a cortex of spinulose branches. 4. 



3. Flabellum uncorticated. 5. 



4. Spinulose branches in close whorls. 43. U. verticillosa. 



\. Spinulose branches subsecund or irregular. 4. U. spinulosa, 

 5. Flabellum plane. 2. U. conglutinata. 



5. Flabellum concavo-convex to cyathiform. 3. U. cyathiformis . 



Page 396, after description of UDOTEA ARGENTEA, add, 



RHIPILIA Kiitzing, 1858, p. 12. 



Uncalcified, green, cuneato-flabellate to excentrically subin- 

 fundibuliform, stipitate, stipe thin, flabellum thick or thin, 

 sometimes zonate, composed of a lax felt of dichotomously 

 branched filaments, often not cylindric, bearing rather short, 

 pseudo-lateral branchlets, each terminating in a 2-6-parted ten- 

 aculum or crown. 



Differs from Udotea by the absence of incrustation ; from 

 Avrainvillea by the terminal tenacula. 



R. TOMENTOSA Kiitzing, 1858, p. 12, PI. XXVIII, fig. i ; 

 Gepp, 1911, p. 55, PI. XV, figs. 126-128; Udotea tomcntosa 

 Collins, 1909, p. 394; Avrainvillea laetevirens Maze". No. 233. 

 Fig. 28. Guadeloupe. 



Forma ZONATA Gepp, 1911, p. 55, PI. XV, fig. 129; Borgesen, 

 1913, p. 93, fig. 76. Stipe more slender than in the typical 

 form, frond round-flabellate or reniform, thin, translucently 

 zonate. Dredged in about 30 meters, Virgin Islands, Borgesen. 



Page 399, after description of HALIMEDA GRACILIS, add, 



Var. OPUNTIOIDES Borgesen, 1913, p. 108, fig. 87. Segments 

 large, up to 14 mm. wide and 9 mm. high, suboval-reniform, 

 often distinctly crenulate on the upper margin or even trilobed. 

 Dredged in about 30 meters, Virgin Islands, Borgesen. 



