57 



a curved plate with a somewhat lobed margin. In some respects 

 these specimens resemble U. subflaccida, but they differ from 

 it by the lateral position of the pyrenoid. As the specimens in 

 some respects differ from the typical U. psetidoflacca, I have 

 referred them to a new form, f. tenuior, which form, although 

 not sharply defined, may, I think, be distinguished from the 

 typical form by the following characters: The chromalophore 

 usually does not fill the length of the cell, sometimes has a 

 lobed margin, and the cells are longer. This form seems to 

 me to be very much like U. implexa Hazen Am. Ulothricaceæ 

 pi. 21, fig. 1, 2). 



The species occurs on stones and rocks in the littoral 

 region. Sometimes it has been collected in fresh water, beneath 

 high-water mark. It is not rarely found in company with V. 

 ftacca, occasionally rather gregarious, forming green strata on 

 the rocks. The species is also found growing on Fucus and 

 Acrosiphonia, and sometimes entangled between other algæ. 

 Specimens with gametangia were gathered in May— July, with 

 zoosporangia in May and July. It occurs both on exposed 

 and sheltered coast. 



f. typica is certainly common in West Greenland. 



Gr. occ: Atanikerdluk, Sarkak in Vajgat (N.H.); Inilik in Ata- 

 nek Fjord (P. H. Sörensen); Holstensborg (N. H.) ; Godthaab (L.K.R.); 

 Frederikshaab (L. K. R., N. H.); Arsuk (H.Lassen); Issa west of 

 Arsuk Fjord, Arsuk Storo (L.K.R.); Upernivik Island near Kagsimiut 

 (H. Lassen); Sydproven, Umanarsuk, the south end of Amitsok 

 opposite Sermersok, Nanortalik, Kimatulivigsalik, Kitsigsut Oer (A. 

 Jessen). 



Gr. or. : Ikerasarsuk (Vahl) ; Smalsund. 



f. tenuior. * 



Gr. or.: Nunatsuk (Sylow). 



Geogr. distribution: Iceland, The Færoes, Norway. 



l. scutata nov. sp. 



The filaments are usually distinctly narrowed at intervals, 

 5 — 6// thick in the lowest part and 9 — 16// thick in the upper 



