Lithothamnion phymatodeum Fosl. mscr. 



Thallus crustlike, 1 — 2 mm. thick, with wart-like or irregular 

 excrescences ; conceptacles of sporangia subprominent, 300 — 350 /j. 

 in diameter. 



The spedes forms crusts on rocks in the upper sublitoral zone. 

 It shows a striking resemblance in habit to Pliymatolithon poly- 

 morphum. I 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 \j. long, 

 forming ascending bows. The perithallic layer is composed of cells 

 which partly are square or almost square, 7—8 /x in diameter, 

 partly and more frequently vertically elongated, 9—11 or up to 

 14 /a long and 6—9 \x 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 /x 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 /x long 

 and 55 fx thick with enduring interwalls. 



