THE GREEN ALGAE OF NORTH AMERICA 285 



have only one species, and that somewhat doubtful, details of 

 development and reproduction being insufficiently known. 



E. ? MOEBIUSIANUM De Toni, 1889, p. 208 ; Stigeodonium sp., 

 Mobius, 1888, p. 239, PI. IX, fig. 3. Disk up to 500 \t. diam., 

 composed of filaments radiating irom a common center ; cells 5 ^ 

 diam., 1-2 diam. long; rising above into a short, papilla-like 

 extension ; occasionally seta-bearing. Fig. 88. Porto Rico. 



The erect filaments are much less developed than in most 

 species of the genus ; Mobius' first supposition may be correct, 

 that it is a species or state of growth of Stigeodonium. 



ii. DERMATOPHYTON Peter, 1886, p. 191. 

 Forming rounded or irregular disks, on the shells of turtles, 

 of closely packed cells in several layers, below sending cunei- 

 form projections into the shell ; asexual reproduction by (bicili- 

 ate ?) zoospores formed by repeated division of the contents of 

 the enlarged cells of the outer layer. 



Only one species. 



D. RADIANS Peter 1886, p. 191 ; D. radicans Potter, 1887, 

 p. 251, PI. VIII. Disks up to 12 mm. diam., composed of 

 squarish cells, originally in branching radial series, but soon 

 united to a parenchymatous layer, several cells thick, except at 

 the margin ; the superficial cells enlarging to form sporangia, 

 from which the contents are discharged in the form of zoospores, 

 the cells below then becoming sporangia, the thickness of the 

 frond being maintained by successive divisions of the cells by 

 horizontal planes. Fig. 93. Mass. Europe. 



The name is wrongly quoted by Potter as D. radicans, and the 

 error has been copied by De Toni, 1889, Wille, 1900, and 

 others ; no one seems to have taken the trouble to look up the 

 original description'. 



12. ULVELLA Crouan, 1859, p. 288. 



Fronds forming small disks on larger plants or other objects, 

 firmly attached by the under surface, originally monostromatic, 

 of radiating, laterally united, dichotomous filaments ; later 

 polystromatic, except at the margin ; cells with parietal chro- 

 matophore and one pyrenoid, arranged in more or less definite 

 vertical series ; biciliate zoospores formed in the central cells, 

 4-8-16 in a cell, escaping by an opening at the top. Marine. 



KEY TO THE SPECIES OF ULVELLA. 



i. On stones and shells. 3. U. lens. 



I. On algae. 2. 



