90 M. FOSLIE. [1905 



Lithophyllum incrustans. The alga is then also more easily at- 

 tacked by animals, and will now and then be detached from the 

 substratum, while elsewhere it is hard attached to it. I have even 

 seen specimens partly detached, with crusts new, but feebly deve- 

 loped, over parts of the side turning downwards. 



The typical form of the species is most vigorously developed 

 and attains to a thickness of up to about 2,5 cm. With this form 

 is connected f. testacea with smaller conceptacles. In both forms 

 the conceptacles are finally overgrown. The form circumscripta 

 is always more faintly developed with conceptacles densely crowded. 

 A form nearly approaching the last mentioned one is f. coalescens, 

 which is smaller and becomes more regularly confluent with con- 

 ceptacles mostly less densely crowded. In both the forms last- 

 mentioned, grown-in conceptacles do not occur. 



As to the structure of the frond, the hypothallic layer is al- 

 ways feebly developed, the cells are 14—30 fi or up to 43 \x long, 

 and 5 — 10 (*■ broad, their length usually being 3 — 5 times the 

 breadth. The perithallic cells are partly squarish, 6 — 10 /->■ in dia- 

 meter, partly and more frequently a little vertically elongated, and 

 9 — 14 fi, or occasionally up to 16 \i long, and 7 — 11 p. broad, 

 the length being up to about V-1% or seldom twice the breadth. 

 Now and then occur cells a little elongated in horizontal direction 

 of the frond. 



The conceptacles of sporangia in f. typica will be developed 

 under favourable circumstances almost over the whole surface of 

 the frond, except a narrow peripherical portion, mostly, however, 

 only a smaller part. They are rather crowded, sometimes irregu- 

 larly scattered, at first visible as light points which gradually be- 

 come decorticated, finally forming shallow holes, impressed pointlike 

 or almost trumpet-shaped, 100—200 fi in diameter, the bottom of 

 which forms a part of the roof and is intersected with 5 — 18 

 muciferous canals. In this form it is usually only the said part 

 of the roof which falls to decay at maturity, sometimes, however, 

 the whole roof is dissolved. In a median vertical section the con- 

 ceptacles are spherical or flattened spherical, 200 — 250 p. in dia- 

 meter. In f. testacea the said conceptacles mainly resemble those 



