NO. 2 DAWSON : MARINE RED ALGAE OF PACIFIC MEXICO 269 



has not been available for examination, and it is not possible at present to 

 elucidate the life history of the plant. In material from Florida distri- 

 buted as P.B.A. 422a, cystocarps were observed to be ostiolate, embedded 

 beneath the cortex, 120-150 /* in diameter, and the carpospore mass aris- 

 ing from a sterile pedicel (auxiliary cell) from which also arises a loose, 

 surrounding basketwork of filaments. The Mexican material is tetras- 

 poric and agrees moderately well in structure and in habit with tetras- 

 poric West Indian material from Tobago Island, although the sporangia 

 are much larger. The subterete, dichotomous branches are distinctive. 



Halymenia bifida sp. nov. 

 P1.2,figs. 19-21;pl. 12,fig. 56 



Thallis 6-8 cm. longis, membranaceis ; laminis brevistipitatis, lineo- 

 lanceolatis, 4-8 (13) mm. latis, 150-200 (260) ju, crassis, simplicibus vel 

 semel bisve dichotomose ramificatis ; apicibus acutis, plerumque bifurcatis ; 

 marginibus integris vel ramulos breves, exiguos, pinnatos ad 1-2 mm. 

 longos habentibus. 



ThalH 6-8 cm. long, membranous, consisting of several linear-lanceo- 

 late, short-stipitate blades from a small discoid holdfast; blades 4-8 (to 

 13) mm. broad, 150-200 (260) jx thick, simple or once or twice dichot- 

 omously branched, the acute apices commonly bifurcate, cuneate at the 

 base to the slender, compressed to flattened, simple or dichotomous stipe 

 which is 400-500 [x in diameter and 2-3 mm. long; margins entire or 

 provided with short, sparse, irregularly spaced, pinnate branchlets 1-2 

 mm. long ; transection showing a dense, pigmented outer cortex, a looser, 

 larger-celled inner cortex, and a medulla of sparse, branched filaments ; 

 outer cortex unistratose, of ovoid cells about 5 fi by 7 /a in dimensions ; 

 inner cortex of about 2 layers of pale, rotund cells 9-16 /a in greatest 

 diameter; branched medullary filaments of elongate to linear cells 4-5 /* 

 in diameter, irregularly, loosely and obliquely crisscrossing the medul- 

 lary cavity, showing some arachnoid cell development adjoining the sub- 

 cortex; cystocarps scattered, embedded, 100-150 /a in diameter, the car- 

 pospore mass compact, subglobose, not conspicuously pedicellate, sur- 

 rounded by a loose perithecial involucre, ostiolate; carpospores ± 

 angular, mostly 14-16 /* in greatest diameter; antheridia not seen; 

 tetrasporangia cruciate, ovoid, 16-18 ft long, scattered through the 

 essentially unmodified cortex. 



Type: Holotype is Dawson 6745, ($), Mar. 13, 1949, on sheet 

 59316, including vial 4177 and slides 2128-2130, in HAHF. 



Type locality: Rock and sand bottom at a depth of 8-15 m., bay 

 adjoining Punta Frailes, Baja California del Sur, Mexico. 



