216 TUFTS COLLEGE STUDIES, VOL. II, No. 3 



of the frond are rather irregularly polygonal with rounded cor- 

 ners ; no noticeable arrangement in longitudinal series ; frond 

 about 30 n thick. 



A species with minute fronds, with more definite outline than 

 is usual in species of this genus. It is known only from Cali- 

 fornia, where it forms a rather dense coating on rocks near high 

 water mark. Hardly enough is known of this plant to decide 

 whether its position is permanently assured. 



3. U. FASCIATA Delile, 1813, p. 153, PI. LVIII, fig. 5; 

 Harvey, 1858, p. 58; P. B.-A., No. 221. Frond divided into 

 more or less linear segments, margin smooth or undulate ; in 

 cross section the two layers of cells separate somewhat at the 

 margin, which is rounded, with a small, open space between 

 the rows. Fla., W. I., Cal. Warm waters all over the world. 



The structure of the frond is similar to that of U. Lactuca, ex- 

 cept the margin, which resembles Enteromorpha linza ; but the 

 shape of the frond, with definite divisions, is quite distinct in the 

 typical form. On the Californian coast, however, it is hard to 

 draw the line between this and U. Lactuca, either from the 

 shape of the frond or from its structure. Even in the typical 

 form there is much diversity as to the divisions of the frond ; 

 they may be dichotomous or apparently lateral ; their width 

 may vary from 5 mm. to 5 cm. ; and the frond may reach a 

 length of a meter ; the margin may be smooth and even, or 

 much crisped and undulate ; in this last it corresponds to forms 

 of Enteromorpha linza. Four forms have been distinguished 

 on the Pacific coast, passing into each other more or less. 



Forma TAENIATA Setchell, P. B.-A., No. 862. Lobes slen- 

 der and elongated, crisped and ruffled ; prominent teeth on the 

 margins near the base of the frond. 



Forma CAESPITOSA Setchell, P. B.-A., No. 809. Divisions 

 numerous, irregular ; fronds intricately entangled, forming a 

 dense coating on the rocks. 



Forma LOBATA Setchell, P. B.-A., No. 863. Lobes short 

 and broad, seldom crisped or ruffled. 



Forma EXPANSA Setchell, P. B.-A., No. L,XXVII. Frond 

 ample, of generally orbicular outline, lobes broad or narrow, 

 more or less sinuous, margin much ruffled ; frond 60-70^ thick, 

 cells somewhat elongate in cross section. 



