
‘ 
Lithothamnion phymatodeum Fosl. mscr. 
Thallus crustlike, 1—2 mm. thick, with wart-like or irregular 
excrescences; conceptacles of sporangia subprominent, 300—350 yu 
in diameter. | 
The species forms crusts on rocks in the upper sublitoral zone. 
It shows a striking resemblance in habit to Phymatolithon poly- 
morphum. 1 do not know the extent of the crust, as I have seen 
but fragmentary pieces. It does not exceed 2 mm. in thickness, 
and the excrescences are frequently rather irregular, in part however 
rised in consequence on covering up extraneous objects. 
The lower part of the thallus is destroyed by worms or other 
animals and, therefore, also the greater part of the primary hypo- 
thallic layer. New hypothallic formations are here and there met 
with; the cells of these are elongated, up to about 18 » long, 
forming ascending bows. The perithallic layer is composed of cells 
which partly are square or almost square, 7—8 yp in diameter, 
partly and more frequently vertically elongated, 9—11 or up to 
14 » long and 6—9 yp broad. On a cross section is occasionally 
to be seen alternating long and short cells. 
Of reproductive organs only sporangia are known. The concep- 
tacles are convex or almost disc-shaped, subprominent, 300—350 
or up to 400 » in diameter seen from above, here and there 
crowded or almost confluent. The roof is intersected with 30—40 
muciferous canals which are crowded in the central part, the latter 
often slightly depressed. This part most often gets dissolved at 
maturity, sometimes the whole roof and, therefore, emptied con- 
ceptacles appear seldom or only in part to be overgrown by new- 
formed tissue. The sporangia are four-parted, about 100 » long 
and 55 p thick with enduring interwalls. 
