92 KJELLMAN, THE ALG OF THE ARCTIC SEA. 
show plainly that the plant is attached at first to some hard object, although after- 
wards, at least in certain cases, it detaches itself and lies free on the bottom. The 
frond has a short, either flattened and upwards broadening, or extremely short and 
almost terete, mainstem, from which there issue repeatedly palmately branching branch- 
systems, spreading like a fan almost in one plane. These are also situated in the 
same general plane, in consequence whereof the plant gets the appearance of a low, 
flat bush. The branch-systems contain axes of at least four degrees, all of which, 
except the ultimate ones, are downwards almost terete, but upwards at the branching- 
point strongly triangularly expanded; fig. 1. The branch-systems are sometimes almost 
free, as is shown by the above-quoted figure, sometimes, in older specimens, more or 
less confluent with one another. It even happens, that branch-systems belonging to 
different individuals growing close to one another, become confluent. The tips of the 
branches, except when they are on the point of dividing, are scarcely enlarged, but 
rounded, or almost truncate. 
The structure of the frond. In this respect the plant coincides so closely with L. 
soriferum, that I need not enter into any detailed description. The figures 3, 4, 5, 
6, 7 exhibit the structure better than words could do, and on comparing them with 
the corresponding figures of £. soriferwm, the similarity of the two species in this re- 
spect is easily perceived. They agree even with regard to the size of the cells. In 
the cup-shaped layers of tissue on a thin median section the cells are 6—10 «. thick 
and 20 uw. long at the most. 
Organs of propagation. Conceptacles of sporocarpia and sporangia are to be found 
on the same individual and on the same branch. They are thinly scattered on and 
below the tips of the branches (fig. 2) and differ very much in shape from each other. 
The conceptacles of the sporocarpia present the form of acute cones, upwards traversed 
by a canal. The conceptacles of the sporangia are flatly hemispherical, about 0,5 . in 
diameter at the base, larger and more elevated than in L. soriferum. They are never 
found to have grown down into older portions of the frond, which proves the growth 
of the frond to take place in the same manner as in the preceding species. The roof 
of the conceptacles of sporangia is intersected by numerous canals, generally 6-sided 
in transverse section, which are filled with a gelatinous substance and whose orificial 
cells differ somewhat in shape from the other surface-cells of the roof. The sporangia, 
fig. 8, are tetrasporic, considerably larger than in L. soriferum, about 250 wv. long and 
100 w. thick, cylindrical, cylindrically spindle-shaped or cylindrically claviform. 
The relation of the present species to others. Amongst the Lithothamnia that I 
know, this species stands nearest to ZL. soriferum, from which it seems, however, to be 
clearly distinguished by its peculiar ramification, its few scattered conceptacles of tetra- 
sporangia and its large sporangia. 
Hab. According to the kind communication of Mr M. Fosuin, the finder of the 
species, it grows in 20 fathoms water, and, as it seems, in sheltered places of the coast. 
Specimens, collected at the beginning of August, have carpospores in development and 
ripe tetraspores. 
