Lithothamnion monostromaticum Fosl. mscr. 



Thallus forming crusts of indetinate shape on Nitopliyllum, 

 monostromatic except in the neighbourhood of the conceptacles. 

 Sporangia-conceptacles subprominent, flattened in the central parts, 

 250 — 400 iJ- in diameter. 



The plant forms at first delicate suborbicular crusts on Nito- 

 phyllum, which little by little become confluent and at length form 

 somewhat extended crusts of indefinate shape. Occasionally new 

 crusts may be formed upon the primary. Judging from a scanty 

 material the species is monostromatic except where reproductive 

 organs appear or are in development. When seen from the surface 

 the cells are partly square with a little rounded corners, 7 — 10 />- 

 in diameter, partly and most frequently more or less elongated, 

 or up to about 15 /^ long. On a vertical section they are somewhat 

 rounded and of about the same diameter as seen from the surface, 

 or slightly elongated partly in horizontal partly in vertical direction. 



The conceptacles of sporangia are at first convex, subpromi ■ 

 nent, circular in circumference or now and then almost oblong 

 when seen from above. Afterwards they frequently appear to 

 become decorticated in the central parts and flattened, or occasio- 

 nally almost disc-shaped, 250 — 400 jj- in diameter and traversed 

 by a number of delicate musiferous canals. The sporangia are 

 four-parted, about 60 /^ long and 30 // broad. The conceptacles 

 of cystocarps are hemispheric-conical, rather low and of about the 

 same diameter as the former. A few smaller conceptacles in com- 

 pany with de preceding are perhaps those of antheridia. 



The species stands nearest to Lithothamnion corticiforme. 

 It is hitherto only known from New Zealand. 



