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 Lithothamnia, 

 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/x long and 4-7/u. 

 broad. In the perithallic layer there is no stratification to be seen. The cells are here 

 partly squarish, often with rounded corners, 5-8p. in diameter, partly and more 

 frequently vertically elongated, and 8-1 2/x, long, with a breadth of 6-8/i. 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 400/x 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, 90-1 20/x long 

 and 40-50/i 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 (tetraspbric) in L. magellanicum. On the other hand, the species in question in 

 some respects reminds one of the Arctic species Lithothamnion Iceve. Sterile specimens 

 can on a superficial examination easily be confounded with Lithophyllum decipiens. 



This is the first species known from the Antarctic 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 

 18 fms. It seems to have been pretty plentiful, as some sixteen pebbles with 

 incrustations of the species were collected. 



