124 Rhodora (ох 
This plant is common on the Lunatia shells at Revere Beach, so 
much so that in spring and early summer it is the exception to find 
а live shell free from it, and at all times it is to be found plentifully. 
It appears to die with the host, for it has never been found on dead 
shells. Its distribution seems to be very limited, as there is no record 
of its occurrence except at this one station, though the Lunatia is 
found all along the coast, and the alga has been sought for carefully 
on the Maine coast and in southern New England. It always occurs 
on the spire of the shell, which in the genus is quite flat; here it forms 
a roundish patch, thickest at the centre, the tip of the spire, and has 
never been known to cover more than a quarter of the surface of the 
shell. ‘The color is a deep rich green, an unusual color in this genus, 
where a yellowish color is general. The substance is dense, and it 
is only by crushing or dissection that the structure can be: made out. 
The basal layer is largely continuous, the filaments showing distinctly 
only at the edges; the erect filaments are short, stout, and of cells 
usually quite irregular in shape; they increase in size upward, but 
rather irregularly, the terminal cell being the largest, with a broad 
rounded top, but not differing otherwise from any other cell of the 
filament; the spores escape through an opening in the summit, as 
in other species. The general appearance is rather that of Gon- 
grosira than of Pilinia. 
P. minor Hansgirg in Foslie, Contribution to Knowledge of the 
Marine Algae of Norway, Tromsé Museums Aarshefter, XIII, p. 146, 
Pl. II, figs. 17-22, 1890. Stratum thin-coriaceous or almost crusta- 
ceous, yellow green, more or less extended. Filaments generally short 
and little branched. Vegetative cells 3-5 x wide, 1-2 times as long, 
end cells rounded; in each cell a parietal band-shaped chromatophore. 
Prof. N. Wille of Christiana has kindly determined the American plant 
as belonging to the species of Hansgirg, of whose original description 
the foregoing is a translation. Our plant, however, seems to be more 
fully developed, so that a more complete account is now possible. 
There is little distinction between horizontal and erect filaments; near 
the substratum there is a densely packed cellular mass, in which it is 
difficult or impossible to distinguish filamentous structure; above 
this short filaments are easily made out, but they are not uniformly 
vertical, and they are quite irregular in size and shape of the cells. 
The latter may be cylindrical, as little as 2 4 diam., but are usually 
larger and not much longer than broad, ovoid or even subspherical; 
