NO. 8 DAWSON : A REVIEW OF THE GENUS RHODYMENIA 129 



Fronds not conspicuously flabellate, mainly dichotomous, 

 narrowly cuneate from the stipes 



Stipes from a discoid holdfast without stolons; type: — 



California R. arborescens 



Stipes with branched stolons augmenting the simple 

 holdfast 



Segments blunt at apices; ultimate segments long 

 Fronds and stipes lobulate-proliferous ; tetraspor- 

 ic apices usually expanded into short, broad lobes ; 



type: — California R. lohata 



Fronds and stipes nonproliferous ; tetraspores un- 

 known; types: — Chile . . . . R. corallina 

 Segm.ents with palmate, polydigitate apices, the ulti- 

 mate segments veiy short, acute; type: — New Zea- 

 land R. palmipedata 



Subgenus EURHODYMENIA nom. nov. 

 Section 1. Pertusae nom. nov. 



Tetrasporic material of only one species was available as a basis for 

 organizing this section, but as far as the descriptions can be interpreted, 

 7 species can pretty definitely be assigned to it. The even distribution of 

 tetraspores over the frond is reasonably distinctive, since members of Sec. 

 Palmatae which have large tetrasporic areas bear them in broken, irregu- 

 lar arrangement. In any case, if Rhodymenia pertusa can be taken as at 

 all representative of this type of tetraspore production, a definite differ- 

 ence can be realized in the cross-sectional appearance of tetrasporic fronds 

 between sections Pertusae and Palmatae. This difference is best shown 

 by the illustrations (figs. 1-4) but may be expressed briefly as : showing an 

 essentially unmodified cortex in Sec. Pertusae; showing a nemathecially 

 modified cortex in Sec. Palmatae. 



(1) RHODYMENIA PERTUSA (Post, et Rupr.) J. Ag., Sp. II 

 (1851), p. 376; Epicr., p. 329; Porphyra pertusa Post, et Rupr., 

 Illust. Alg. (1840), p. 20, tab. XXXVI. 



Plate 18, Figs. 1-2 

 Distribution. — The type specimen from Kamchatka; in the Arctic 

 Ocean; Greenland; Spitzbergen; North Japan; Bering Sea; Coast of 

 North America south to Puget Sound, Washington. 



