85 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 12 



SPHACELARIA Lyngbye, 1819 



Sphacelaria mexicana n. sp.®^ 

 Plate 3, Figs. 1-8 



Plants forming considerable mats, 2.5-4.0 mm high, the erect filaments 

 arising from a disciform base, sparingly alternately branched, the branches 

 erect, to 25-48 /a diam., rather less in the branches ; hairs arising near the 

 tips of the axes, short and soon lost, about 15 fi diam.; gametangia and 

 sporangia unknown ; propagula on short pedicels, bicornute, with convex 

 sides and short obtuse slightly produced arms, to 86-120 /t broad, 72 /* 

 long excluding the stalk. 



This species seems related to S. tribuloides Menegh. (Taylor 1928, p. 

 106, pi. 14, figs. 7-10), but the base is different. It resembles S. brevicorne 

 Setchell & Gardner (1924, p. 725, pi. 19, figs. 59, 60), except that it is 

 bicornute and has a disciform base, is lithophilous instead of epiphytic, 

 branches more freely and has propagulae with shorter body and more 

 contracted arms. Sauvageau's (1900-1914, p. 132, fig. 31) S. cornuta has 

 much longer arms. 



Mexico: Is. Revilla Gigedo, on rocks in the littoral zone, Braith- 

 waite Bay, I. Soccoro, no. 34-7 (TYPE), 2 Jan. 1934. 



Dictyotaceae 



Plants of moderate size, one to several axes arising from a cushionlike 

 holdfast, or rarely decumbent; usually stupose at the base but without a 

 specialized stalk, though often eventually with the old, denuded portion 

 appearing subterete and stalklike; above dividing into a flat bladelike part, 

 which may be filiform or expanded, strap shaped or cuneate, fan shaped 

 or reniform; growing from a single apical cell or from a marginal row of 

 growth initials, forming a parenchymatous blade ; reproductive structures 

 scattered or in sori on the surface, developed outwardly from the surface 

 cells; asexual reproduction by tetraspore; sexual reproduction by an- 

 therozoids and eggs. 



KEY TO GENERA 



1. Thallus without a midrib, or at most the midrib short and rudi- 

 mentary 2 



^'^ Sphacelaria mexicana n. sp. — Planta implexa, ad 2.5-4.0 mm altitudine, 

 filamentis erectis e basibus disciformibus natis, polysiphonis, ramificatione alterna, 

 ad 25-48 j.1 diam.; propagulis in pediculis brevibus sitis, bicornuatis, lateribus con- 

 vexis, brachiis brevibus obtusisque, paululum productis, 86-120 \i lat., 72 n long. 

 Planta typica in loco dicto Braithwaite Bay, I. Soccoro, Mexico, legit W. R. 

 Taylor no. 24-7, 2 Jan, 1934. 



