No. 3] REMARKS ON NORTHERN LITHOTHAMNIA. 35 



diameter, by a thickness of about 5 cm. Conceptacles of sporangia 

 convex, but little prominent, often crowded in the upper part of 

 the branches, 300 (250)— 400 />- or up to 500 \i in diameter; 

 sporangia bisporic, 140—220 //■ long, by 60 — 100 p. broad; con 

 ceptacles of cystocarps conical, 300—400 \i in diameter. 



f. pusilla Fosl. mscr. 



Frond 1—2 cm. in diameter, branches crowded, subsimple, 

 shorter and sometimes thinner than in the typical form. 



Syn : Lithothamnion colliculosum Batt. in Grevillea vol. 21 (1892), p. 23, 

 partim! Batt. Cat. Brit. Alg. (1902), p. 97, partim ! De Toni, Syll. Alg. IV (1895), 

 p. 1732, partim. Non Fosl. in Rosenv. Deux. Mem. Alg. Mar. Gronl. (1898), p. 11. 



Lithothamnion roseum Batt. in Grevillea, vol. 22 (1893), p. 20, saltern 

 pro parte! 



Lithothamnion fasciculatum Aresch. Obs. Phyc. 3, (1875) p. 5, partim! 



This species — as it was formerly circumscribed — included 

 partly young or stunted specimens of the species in the sense here 

 taken, partly young L. glaciale. The essential part of the material 

 I have hitherto seen of this alga consists of such young specimens, 

 often hardly distinguishable from certain forms of L. glaciale and 

 L. Granii. I have, however, lately received specimens which, I 

 think, are representing an old form of the species in the sense taken 

 above. This form even approaches L. fornicatum in habit. 



At first the species is hard attached to the substratum, rocks 

 or stones, it often forms a crust widely spread, but mostly attaining 

 to no conciderable thickness. In the lower part of the litoral region 

 or in the upper part of the sublitoral region the crust mostly 

 develops only simple or bifid branches, which are frequently rather 

 crowded and straight, 2 — 3,5 mm. thick with rounded ends. If 

 the crust is attacked by animals, the alga is gradually detached 

 from the substratum and becomes more densely branching. Farther 

 down in the sublitoral region, it becomes — under favourable 

 circumstances — much larger and more branching. The crust 

 disappears little by little, being attacked by animals, and the branches 

 are repeatedly divided, but still rather straight. Finally the alga 

 will become almost inverted-plate-shaped and then resembles certain 

 forms of L. fornicatum. 



