20 M. -FOSLIE. [1899 



forms in L. Muelleri^ but on the other hand do not show transi- 

 tions as in the latter. Besides, in f. imbricata the conseptacles 

 are more densely crowded and the roof often not depressed in 

 the centre. 



The plant is known from Cape Jaffa, South Australia, appa- 

 rently scarce. Dr. Aug. Engel har t. 



In Thuret's (Bornet's) herbarium I have seen a specimen of 

 f. umbonata labelled „Australie?", showing that the spedes probably 

 is not quite local. 



Lithothamnion tenuissimum Fosl. mscr. 



Thallus crustlike, attached to stones, smooth or nearly so, of 

 indifinite extent, 100 — 250 /j. thick. Conceptacles of sporangia 

 scattered or somewhat crowded, convex and slightly prominent, 

 180—200 p- in diameter. Sporangia four-parted, 75 — 90 ij. long 

 and 50 — 55 y. broad. 



The species at first forms small, very delicate, partly orbicular 

 partly irregular crusts most often with crenulate margin, in a young 

 state very much resembling a Melobesia, or Lithothamnion mem- 

 branaceum in habit, with subpellucid thallus. However, it fre- 

 quently soon increases in thickness as well as circumference, at 

 length attaining a thickness of 100 — 250 /^., or when two crusts 

 growing over each other occasionally up to about 400 p- thick. 

 If there are more than one crust founded on the same substratum 

 they soon become confluent, partly with limits visible in the shape 

 of very small ridges partly fuUy anastomosing, or now and then 

 the one crust stretches itself over the other. It elings firmly to 

 the substratum, and at length forms crust-complexes of indefinite 

 extent. The surface is smooth or provided with scal}^ thickenings, 

 in an old stage sometimes finely rugged, and the marginal portions 

 now and then with indistinct concentric striæ. 



The conceptacles of sporangia partly are scattered partly more 

 or less crowded, convex but slightly prominent, seen from above 

 180 — 200 // in diameter, and the roof intersected with about 10 

 very delicate muciferous canals. The sporangia are four-parted, 

 75 — 90 // long and 50 — 55 /j. broad. 



