284 KJELLMAN, THE ALGH OF THE ARCTIC SEA. 
Pylaiella nana nob. 
P. thallo maculam minutam, diametro 1 mm. in aliis algis formante, e filis repentibus, in membranam 
fere confertis, fila verticalia, cylindrica emittentibus contexto; zoosporangiis seriatis, gametangiisque seepe ramo- 
sis, cylindricis vel elongato-conicis fila verticalia terminantibus. Tab. 27, fig. 13—17. 
Description. In its vegetative system this alga much resembles an Ectocarpus 
terminalis or . reptans. As in these species the frond is formed of branching cell- 
rows creeping on other alge, densely compressed, throwing out at right angles un- 
branched or very little branched cell-rows. These vertical cell-rows are of three 
kinds. Some of them are almost quite cylindrical, composed downwards of cells rich 
in endochrome, upwards of cells that are poor or altogether wanting in endochrome. 
Other rows end in organs that resemble the gametangia of Hctocarpi and undoubtedly 
are of that nature. Those of the third kind are usually slightly claviform, ending in 
a simple or branching row of spherical or short tun-shaped cells, which possess a dense, 
very profuse endochrome. I am not quite clear as to the nature of these rows of cells, 
but they resemble the rows of young zoosporangia in a Pylaiella so much that I cannot 
but regard them as yet as organs of that kind.. 
The procumbent filaments are composed of cells that in longitudinal section are 
rectangular, or square, or from five-angular to polygonal, rich in endochrome and with 
rather thick walls, like the other cells of the frond. The vertical cell-rows issue from 
the inner part of the disk formed of those densely compact filaments. Those vertical 
rows which are sterile are about 750 “. in length and 15 w. in thickness, usually un- 
branched, composed of cylindrical cells that are from one to one and a half time as 
long as thick. 
The gametangia are almost always branching, though not much, and elongated- 
conical, 80 «. long, 20—25 wu. thick. The gamets pass out through a hole formed in the 
top of every gametangium (fig. 14). The chains of zoosporangia are usually unbranched, 
composed of from three to more zoosporangia (fig. 15—16), sometimes rather much bran- 
ching. Every branch is formed of one or more zoosporangia, which are different in shape, 
usually almost spherical, short cylindrical or tun-shaped. Their walls are thicker than 
those of the vegetative cells. I have not seen zoosporangia with fully developed zoo- 
spores (fig. 15—17). 
If this alga is really a Pylaiella, it is sharply distinguished from all hitherto 
known species of this genus by its smallness, by the structure of its vegetative system, 
and the shape of its gametangia. 
Habitat. It grows scattered within the litoral zone in exposed places, epiphytic 
on Cladophore, and has been found with gametangia and sporangia in August. 
Locality: The Norwegian Polar Sea: Gjesver in Finmarken. 
