NO. 1 DAWSON : MARINE RED ALGAE OF PACIFIC MEXICO 139 



The strictly cylindrical, crooked, tumorous branches with thick 

 cortex and constictions at the genicula are distinctive of this species. 



Amphiroa subcylindrica sp. nov. 



Plate 29, fig. 1 



Amphiroa rigida Lamx., as interpreted by Dawson, 1944, p. 276, 



Thallis crasse rosulatis, 6-8 cm. altis, ramificatione irregulariter 

 dichotoma, plus minusve multifaria; segmentis magnopere calcificatis, 

 teretibus, cylindricis vel subcylindricis, plerumque 1.0-1.3 mm. (vel ad 

 2 mm.) diametro, simplicibus vel furcatis; geniculis crassis at saepe plus 

 minusve calcificatione magna tectis; cortice intergeniculari crassa; con- 

 ceptaculis in segmentis vetustis alte infixis et in gradibus compluribus 

 continuis. 



Thalli saxicolous, erect, coarsely tufted, 6-8 cm. high, consisting of a 

 few abundantly branched primary branches from the crustose stratum; 

 branching irregularly dichotomous, more or less multifarious, at inter- 

 vals of 1-2 segments; segments heavily calcified, smooth, cylindrical or 

 subcylindrical, occasionally compressed or even flattened, mostly 1.0-1.3 

 mm. in diameter but often up to 2 mm. thick in some lower parts, the 

 coarsest ones showing constrictions at the genicula, simple or forked, 

 with the genicula well above the forks, 4-12 mm. long (mostly 6-10) ; 

 apices truncate; genicula prominent internally, but often more or less 

 concealed by the heavy calcification, sometimes externally prominent, 

 multizonal, of 3-5 or more tiers of cells, usually including a tier of short 

 cells distally, the cells without oblique end-walls; intergenicula in tran- 

 section characteristically showing a thick cortex of 10 or more layers of 

 very small cells, this cortex undergoing secondary growth and becoming 

 very thick in old parts, the medulla of alternating tiers of long and 

 short cells, but the arrangement variable, commonly 3-5 rows of long 

 cells alternating with a row of short cells ; tetrasporangial conceptacles 

 scattered around branches, embedded or sometimes causing a slight eleva- 

 tion of the surface, in old segments occurring deeply embedded in several 

 successive layers indicative of past reproductive seasons, 200-250 (300) 

 /A in diameter, strongly dorsiventrally compressed, the single pore usually 

 calcified over and not visible from the surface; tetrasporangia borne 

 among prominent, coarse paraphyses, obscurely divided ; sexual plants 

 not observed. 



Type: Holotype is Dawson 555, Feb. 13, 1946, on sheet 4277 in 

 HAHF. 



