2 M. FOSLIE. 
crusts often become a little uneven and finely rugged on the surface by growing over 
small extraneous objects. Besides, in most of the specimens collected the surface of 
the crust is somewhat rubbed, probably owing to the friction of the water by a rather 
strong current. A similar appearance is often to be seen in northern Lithothamnaa, 
particularly in sounds where the tides run strongly. 
In a vertical section of the crust the basal hypothallic layer is distinctly, but not 
strongly, developed, and the convergence of the lower anticlines of this layer towards 
the substratum is very feeble or wanting. The cells are 12-18 long and 4—7p 
broad. In the perithallic layer there is no stratification to be seen. The cells are here 
partly squarish, often with rounded corners, 5-8 in diameter, partly and more 
frequently vertically elongated, and 8-12 long, with a breadth of 6-8. Here and 
there are to be seen cells with the longest diameter in the vertical direction, always, 
however, in very small numbers in proportion to the squarish or vertically elongated 
ones. The cell-walls are frequently rather thick. 
As regards the organs of reproduction, the cystocarpic conceptacles are somewhat 
crowded, subhemispheric-conical, but not quite superficial, as is frequently the case in 
this genus, 300-350 or up to 400m in diameter, when seen from the surface. They 
have been found only in one specimen, and most of them are in a state of decomposition. 
In a few other specimens conceptacles of sporangia occur, They are in some cases 
rather scattered here and there in the crust, in others somewhat crowded, convex, and 
but little prominent, often when older almost disc-shaped, 300-400, in diameter seen 
from above. The roof is intersected with about thirty to forty muciferous canals, which 
are crowded in the central portions. The sporangia are two-parted, 90-120 long 
and 40-50. broad. These organs were ripe in the latter half of January. However, 
the greatest number of conceptacles observed were dissolved, leaving a shallow hole 
or a cup-shaped scar, which later on becomes effaced by new-formed tissue. Once I 
met with overgrown conceptacles in the thickest part of a crust, showing that these 
organs may become fully dissolved only in the thinner and rather young specimens. 
The present species stands nearest to Lithothamnion magellanicum, the latter, 
however, being a coarser plant with, as a rule, larger and more prominent conceptacles 
of sporangia and frequently larger cells. Besides, the sporangia are always four- 
parted (tetrasporic) in L. magellanicum. On the other hand, the species in question in 
some respects reminds one of the Arctic species Lithothamnion leave. Sterile specimens 
can on a superficial examination easily be confounded with Lithophyllum decipiens. 
This is the first species known from the Antaretic regions bearing two-parted 
(bisporic) sporangia. Such were hitherto only known in some species of the genus in 
question from the Arctic regions. 
The plant was collected off Cape Wadsworth on Coulman Island, near South 
Victoria Land, about 73° 30'S., 170° W. Here it was picked up from a depth of 
ig fms. It seems to have been pretty plentiful, as some sixteen pebbles with 
incrustations of the species were collected. 
