494 University of California Publications in Botany [ VoL - 8 



ments from them. It does not seem desirable to separate the Litho- 

 derma series of genera and species from the Ralfsia series since both 

 may be considered as derived from the Myrionemataceae, the sporangia 

 being transformed vertical filaments in the Ralfsia series and only the 

 transformed terminal cells in the Lithoderma series, while the game- 

 tangia may be either terminal or on short lateral branches in the 

 Lithoderma series, but terminal in the Ralfsia series, so far as known. 



Key to the Genera 



1 . Zoosporangia included, borne at the bases of the pa raphyses 2 



1. Zoosporangia superficial, terminal on the erect filaments.. 12. Lithoderma (p. 500) 



2. Thallus entire, or with rounded simple lobes 10. Ralfsia (p. 494) 



2. Thallus deeply and narrowly lobed 11. Hapterophycus (p. 499) 



10. Ralfsia Berk. 



Thallus forming flat expansions of indefinite size and more or less 

 circular outline, at least at first, only slightly and broadly lobed at 

 the margin, never dissected into deep and narrow lobes; either attached 

 firmly to the substratum or later separating largely from it, composed 

 at first of a single basal layer of few to many cells in thickness, but 

 later developing closely packed vertical filaments more or less tightly 

 cohering and covered by a common cuticula, those in fertile areas, 

 "sori," later becoming free and rupturing the cuticula; hairs in 

 minute tufts, scattered, projecting beyond the upper surface of the 

 thallus, generally at least in funnel-shaped depressions; zoosporangia 

 lateral, at the bases of the free filaments, "paraphyses" ; gametangia 

 terminal or subterminal, on the erect filaments or lateral from near 

 their tips. 



Berkeley, in Engl. Bot., Suppl., vol. 3, 1843, pi. 2866; Stragidariir 

 Stroemfelt, Om Algenveg. vid Islands Kuster, 1886, p. 49. Mesospora 

 Weber van Bosse, Not. sur quelq. gen. nouv., 1910, p. 27. 



We have taken the genus Ralfsia in the original sense and as includ- 

 ing the genera Stragidaria Stroemfelt and Mesospora Weber van 

 Bosse, relying on the habit chiefly to characterize the genus and assign- 

 ing the variations in thickness, position of the gametangia, and aggre- 

 gation of the zoosporangia to distinguish the species, or at most, the 

 sections of the genus. We have been influenced to this point of view 

 by our experience with the variability in these respects among the 

 species of the Ectocarpaceae and the Myrionemataceae. The type of 

 the genus is Ralfsia fungiformis (Gunn.) S. and G. (Fucus fungi- 

 f or mis Gunn.). 



