NO. 1 DAWSON : MARINE RED ALGAE OF PACIFIC MEXICO 101 



1000 ju,, attached at first by pluricellular rhizoids especially near the 

 growing margins, then by masses of downwardly growing tissue pene- 

 trating and filling crevices in the substrate, without a distinguishable 

 hypothallus, showing in radial section a mesothallus region giving rise 

 to an inferior perithallus of descending cell-rows extending into the 

 crevices of the substrate, and a superior perithallus of ascending cell 

 rows, these cell rows branched and in part tending to interlace, except 

 in the uppermost part of the superior perithallus composed of cells 10- 

 15 JU, wide and 4-8 times as long; upper superior perithallus cells be- 

 coming progressively shorter, narrower and more regularly arranged 

 in vertical rows toward the upper surface, ultimately 4-6 fx, broad and 

 only slightly longer; tetrasporangial nemathecia sunken so that the top 

 of the paraphyses scarcely extends above the level of the surrounding 

 vegetative thallus parts, 120-130 /* deep, 1 mm. or more broad; para- 

 physes unbranched, very slender, 3.5 ju, wide or less, slightly clavate, 

 mostly of 7-8 cells which are progressively shorter and broader toward 

 the apex; tetrasporangia elongate-ovate, 45-50 fi long, 18-20 fj. wide; 

 sexual reproduction not seen. 



Type: Holotype is Dawson 3841, Feb. 2, 1947, in box 56284, in 

 vial 2344 and on slides 1838-1855, 1866-1867 in HAHF. 



Type locality: On granitic outcrop, southeast side of Bahia de 

 Acapulco, Guerrero, Mexico. 



This species differs from Ethelia australis (Sond.) W. v. B. in struc- 

 ture and in habit, from E. fosltei W. v. B. in structure and in tetra- 

 sporangial characters, from E. biradiata (W. v. B.) W. v. B. in the 

 presence of rhizoids, from E. vanbosseae Feldmann in perithallus cell 

 shape and in the absence of fissures when dry, and from E. pac'tfica B</)rg. 

 in the greater size of the lower perithallus cells. 



Peyssonelia squamaria (Gmelin) Decaisne 



Decaisne, 1841, p. 141, pi. 5, figs. 16-17; Kiitzing, 1869, Tab. Phyc, 

 19: pi. 87a-b; Nageli, 1847, p. 248-250, pi. 19, figs. 9-25. Fucus squa- 

 marius Gmelin, 1768, p. 171, pi. 20, figs. lA-B. 



Thalli subfoliaceous, consisting of prostrate, lobed, more or less 

 superimposed, flabellate blades 3-5 cm. broad attached loosely to the 

 substrate (sponge) by multitudes of long, multicellular rhizoids, 100 

 -250 /A thick, scarcely calcified, in transection showing a mesothallus 

 layer of flattish, horizontal cells giving rise on its lower side to a single 

 perithallus layer from which the numerous rhizoids are produced, and on 



