1920] Setchell-Gardncr : Chlorophyceae 295 



it is very common, discoloring most of the plants of Porphyra in the 

 neighborhood of the Puget Sound Marine Station, while in other years 

 it is difficult to find any plants at all. 



.'^0. Ulvella Crouan 



Thalli forming small disks on larger plants or other objects, firmly 

 attached by the under surface, unistratose at first, later, at times, 

 pluristratose, of radiating, laterally united, dichotomous filaments; 

 segments multinucleate, with parietal chromatophore and no pyre- 

 noid ; 2-ciliated zoospores formed in the central cells, 4-8-16 in a cell, 

 escaping by an opening at the top. 



Crouan, Notice sur quelq. nouv. algues mar., 1859; p. 288, pi. 22, 

 f. E ; Wille, Nachtrage, 1909, p. 89. 



The genus Ulvella is based upon Ulvella Lens, found growing upon 

 bits of porcelain and glass at Brest, France. The original specimens 

 have been examined by Huber (1893, p. 295), who has figured the 

 type {loc. cit., pi. 11, f. 4-6) and added to our knowledge of its 

 morphology and cell structure. It is a prostrate, unistratose or 

 paucistratose, discoid plant composed of radiating filaments with no 

 trace of hairs and whose terminal cells fork before dividing. The 

 chromatophore is single and devoid of a pyrenoid. Nothing is known 

 of the reproduction of the type of the species. It has come to be 

 generally accepted that Dcrmatophyton radians Peter, a species inliab- 

 iting the carapaces of fresh water tortoises in southwest(^rn Europe, 

 is also to be referred to Ulvella (cf. Schmidle, 1899, Wille, 1909, 

 p. 89) and the characters of multinucleate "cells" and 2-ciliated 

 zoospores considered to be characteristic for the genus. Unfortunately, 

 we do not know whether these characters hold for the type species, 

 Ulvella Lens. We also unfortunately do not know whether they hold 

 for the single species of our coast which we are inclined to refer under 

 this genus and also to Ulvella Lens. It is to be hoped that further 

 information may be obtained at some favorable opportunity. 



Ulvella Lens Crouan 



Plate 33 



Thallus orbicular, briglit green, 150-250/x, up to 1.5 mm. diam. ; 

 marginal segments usually cuneate, 3.5-4.5/i, diam., 15-25/x long with 

 terminal growth, central segments 8-15/i, diam. 



Growing firmly attached to Laurencia sp. in the upper sublitloral 

 belt. Central California (Pacific Grove). 



