NO. 1 DAWSON : MARINE RED ALGAE OF PACIFIC MEXICO 69 



Thalli saxicolous, to 20 cm. high, consisting of many erect fronds 

 from a tangled holdfast of stolonoid branches; erect primary axes per- 

 current, below compressed, 1.5-2.3 mm. in diameter and about 1 mm. 

 thick, above 1.5 mm. wide and 350 /x thick, sparingly branched, but pro- 

 ducing in upper parts an abundance of closely set pinnate branchlets of 

 three orders, these progressively smaller in diameter than the main axis 

 and becoming deciduous in older parts 2-4 cm. back of the tips so that 

 older axes are nude except for persistent peg-like bases of some of the 

 branchlets; pinnate branchlets irregularly alternate, averaging about 1 

 mm. apart, somewhat constricted at the base, sometimes a little geniculate 

 at first, but normally standing at about a 60° angle from the bear- 

 ing axis; transection showing a medulla of cells ranging from 7 to 16 

 fi in diameter; rhizoidal filaments sparse in the medulla, congested in a 

 subcortical zone about 45 /a wide; cystocarps and antheridia not observed; 

 tetrasporangia borne in vaguely decussate rows in ovate sori occupying 

 the expanded and rounded or pointed ends of short ultimate branchlets. 



Type: Holotype is Dawson 3413, November 9, 1946, on sheet 

 54673, including vial 2122 and slides 1315-1316, in HAHF. 



Type locality : At mean low water and below on a granitoid reef, 

 Cabeza Ballena, Baja California, Mexico. 



Additional material: Same locality, D. 6795, March 11, 1949. 



This is the largest and coarsest species thus far obtained from tropical 

 waters along the Mexican coast. In gross appearance it is somewhat sug- 

 gestive of Gelidhim crispum Howe or G. cartilagineum (L.) Gaill., but 

 is distinct in several ways from these and other Pacific species: in its 

 very closely set and alternately arranged small branchlets of the second, 

 third, and fourth orders, in the deciduous nature of these leaving the 

 older axes nude except for peg-like remnants, and in the very small, soli- 

 tary, ovate tetrasporangial sori on the ends of non-cordate, ultimate 

 ramuli. 



On all of the material collected thus far there is an abundance of 

 attached animal organisms (bryozoa, sponges, hydroids, etc.) as well as a 

 heavy encrustation of a coarse, brittle melobesioid. 



Gelidium papenfussii Loomis 

 Plate 5, fig. 3 



Loomis, 1949, p. 1, pis. 1,2,3,8. 



Thalli saxicolous, to 16 cm. high, consisting of several to many erect 

 fronds from a holdfast of entangled, adherent stolons ; erect fronds con- 

 sisting of a more or less percurrent, complanate, primary axis 0.6-0.8 mm. 



