1919] Setchell-Gardner : Myxophyceae 31 



Key to thk Species. 



1. Cell wall thin, iiiconsipicuous 2 



1. Cell wall thicker, cmispicuous 3 



2. In extended colonies of 1-several layers 1. X. acervatus (p 31) 



2. Solitary or in small colonies of 1 layer 2. X. Gilkeyae fp 32) 



3. Cells more or less elongated in horizontal diameter, polymorphic 



5. X. Chaetomorphae (p 35) 



3. Cells not elongated in horizontal diameter 4 



4. Cells forming continuous layers, cell walls often diffluent, fjonidia 1 5-2/* in 



diam 3. X. Cladophorae (p 33) 



4. Cells in small colonies, cell walls dense, not diffluent, gonidia 2.8-3.5/x in 

 diam 4. X. pyriformis {p 34) 



1. Xenococcus acervatus S. and G. 

 Plate 5, fig. 13 



Cells wholly epiphytic, dividing in t^v() planes perpendicular to 

 the host, building colonies at first one cell deep, later confusedly 

 heaped uj), of indefinite extent; cells angular at first, soon becoming 

 spherical or pear-shaped, 3-6/x diam., cell wall thin, hyaline; proto- 

 plast homogeneous, pale blue-green; gonidangia unknown. 



Growing in great profusion on Enteromorpha sp. in salt marsh 

 pools. San Francisco Bay, California. 



Setchell and Gardner, in Gardner, New Pac. Coast Alg. Ill, 1918a, 

 p. 459, pi. 39, fig. 13. Pleurocapsa amethyst&a var. Schmidtii Collins, 

 in Collins, Holdcn and Setchell, Phyc. Bor.-Amer. (Exsicc), no. 1704. 



The first publication of the name P. amsthystea var. was by Bor- 

 gesen (Mar. Alg. Fiier., 1902, p. 524), Johannus Schmidt having 

 identified one of Borgesen's species from the Fiieroes as belonging 

 there. Borgesen stated that Schmidt would comment on the species 

 later in Helgi Jonsson's paper. Jonsson's paper appeared in 1903 

 btit Schmidt mentions only a plant from Iceland under the above 

 name {"P. (unethystm var."). Collins {loc. cit.) considers our plant 

 to be of the same variety as the Iceland plant and gives it a varietal 

 name without furtlx-r comment. 



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

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

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

 variety of that species growing in Iceland, determined by Schmidt 

 {in Jonsson, 1903, p. 378). There are no specimens of either of these 

 available at present for comparison. Rosenvinge 's figures and descrip- 

 tion of P. (unethysfea show plainly that the cells divide in three planes, 

 which places it witli tln' genus Pleurocapsa. Schmidt states that the 



