No. 3] REMARKS ON NORTHERN L1TH0THAMNIA. 29 



form subsimplex is a form less independent, which is on one side 

 approaching f. typicd, but the crust forms no lobes or but indi- 

 stinct and small ones, and the branches form no bundles. It may 

 be parLly vigorously developed, forming a thick crust with shorter 

 or longer branches, partly forming a thin crust with branches feebly 

 developed. In certain stunted forms of L. glaciate the crust is 

 about 3 mm. thick with a surface but indistinctly verrucate or 

 almost even, approaching Phym. compactum or LitJwth. foecundum 

 in habit. Cp. under the latter species. 



The form subfastigiata is also varying and often rather di- 

 verging. It frequently encompasses pebbles forming smaller or 

 larger nodules, or is attached to rocks. Lithoth. glaciale, like 

 several other species, has a tendency to detaching itself from the 

 substratum, particularly when it is small, or when the basal crust 

 is attacked by animals, which is of frequent occurence particularly 

 in f. subfastigiata, sometimes also in f. typica, and which is per- 

 haps to be regarded as the chief cause of the loosening. When 

 attached to rocks, the crust is often detaching itself at a rather 

 early stage of development, and at the same time small lobes are 

 formed, the ramification becomes denser, the branches more or less 

 fastigiate and rather coalescing, with wartlike processes. At last 

 the alga is completely detached from the substratum, and under 

 favourable circumstances the part turning downwards is covered 

 with a new crust, mostly a quite thin one, from which short 

 branches are emitted. When the form is encompassing pebbles, 

 the crust is often but faintly developed, and branches are emitted 

 at an early stage such as in some other species which are nor- 

 mally attached to hard objects. 1 ) Also in this case small lobes 

 are formed, but even these are partly dissolved by boring mussels, 

 the branching grows dense, and the branches short, sub fastigiate, 

 usually forming small bundles, more or less approximate. It is 

 often not distinguishable from certain forms of L. intermedium 

 but for the panition of sporangia, and sometimes it bears a con- 



!) Cp. M. F o s 1 i e. Die Lithothamnien des Adriatischen Meeres und Marokkos. 

 Wissensch. Meeresuntersuchungen. Neue Folge. VII Band. Abt. Helgoland. 

 Heft. 1. 1904. Pag. 8. 



