460 University of California Puhlicatioiis in Botany [Vol. 6 



or pear-shaped, 3-6/a diam., cell wall thin, hyaline ; protoplast homo- 

 geneous, pale blue-green ; gonidangia unknown. 



Growing in great profusion on Entcromorplia sp. in salt marsh 

 pools. San Francisco Bay, California. Type no. 1580, Gardner. 



Plcurocapsa amicthystea var. Schmidtii Collins, in Collins, Holden 

 and Setehell, Phyc. Bor.-Amer. (Exsicc), no. 1704. nomen novo. 



The first publication of the name P. amethyst ca var. was by B0rge- 

 sen (Mar. Alg. Faer., 1902, p. 524), Jobs. Schmidt having identified 

 one of B0rgesen's species from the Faeroes as belonging there. B0rge- 

 sen stated that Schmidt would comment on the species later in Helgi 

 Jonsson's paper. Jonsson's paper appeared in 1903 but Schmidt men- 

 tions only a plant from Iceland under the above name {P. amethyst ea 

 var.). Collins {loc. cit.) considers our plant to be of the same variety 

 as the Iceland plant and gives it a varietal name without further 

 comment. 



In the absence of gonidangia it is not at present possible to give a 

 complete comparison of onr plant with the description of the Green- 

 land plant, P. amethystea, of Kosenvinge (1893, p. 968), nor with the 

 variety of that species growing in Iceland, determined by Schmidt 

 (1903, p. 378). There are no specimens available to me at present 

 for comparison. Rosenvinge's figures and description of P\ amethy- 

 stea show plainly that the cells divide in three planes, which allies it 

 with the genus Pleurocapsa. Schmidt states that the Iceland plant 

 difi'ers from the the Greenland plant only in color, but forbears nam- 

 ing it on that character alone. The Iceland plant is thus a Plcuro- 

 capsa. Our plant divides vegetatively in but two planes, and, ac- 

 cepting Thuret's understanding of his genus Xenococcus, it belongs 

 to that genus rather than to Plcurocapsa. A brief discussion of the 

 structure and relation of these two genera was given in my paper 

 (New Pac. Coast Mar. Alg. II, 1918, p. 429). 



Xenococcus acervatu^ differs from P. amethystea in the number of 

 planes of vegetative cell divisions, in the shape and size of the cells 

 and in their color, the color of the latter being "sordide violacea," 

 and of the former pale blue-green. None of the seven illustrations of 

 Rosenvinge {loc. cit.) resembles very clearly any phases of the de- 

 velopment of our plant except "A," the surface view of a group of 

 vegetative cells. 



At times the cells as viewed in the median plane of the host plant 

 are piled up several cells deep, as though they had arisen by horizontal 

 divisions. If this were the case our plant would ])roperly belong to 

 the genus Pleurocapsa. This does not seem to be the case, however, as 



