40 M. FOSLIE. [1903 



Lithoth. pi. 12, fig. 1. It is in general freely developed at the 

 bottom, seldom attached to pebbles or shells of mussels and then 

 at first developing a thin crust. Of this form there are found a 

 more delicate and more southern one, and a coarser and more 

 northern one, the latter of which runs into f. robusta. On the 

 other hand f. sub splicer ica imperceptibly runs into f. dimorpha, of 

 which also a coarser form (L. dimorplmm, Noiw. Lithoth. pi. 10) 

 and a somewhat more delicate form (L. TJngeri f. fastigiata, Notw. 

 Lithoth. pi. 5) are found. The latter is met with chiefly in shallow 

 sounds where the current is strong. It is distinguished for very 

 short and rather coalescing branches. The form sometimes en- 

 compasses small pebbles, but always develops only a very feeble 

 crust with crowded branches proceeding from it, or occasionally 

 attaches itself to or encompasses stones in a stage of development 

 somewhat advanced. The central parts of this form nearly always 

 are gradually attacked and dissolved by boring mussels, and finally 

 an opening is formed. It is a rather stunted form of the species 

 and never attains to any considerable size. The form apiculata 

 is perhaps also a stunted or but a young form of the species. This 

 form partly runs into the preceeding one, partly also approaching 

 f. tuberculata as to ramification, in the latter case with the branches 

 of the central parts rather coalescing, giving the impression of small 

 lobes, and those of the last order forming small bundles. 



The form obcrateriformis is developed from f. subphwrica r 

 which is mostly only found in places peculiarly favourable to the 

 development of the alga. Also f. subsphcerica is much attacked 

 particularly by boring mussels, which first destroy the central parts 

 of the alga and continue their destructive work outward towards 

 the peripheric parts, which are often only forming as it were a 

 thin cover round the said animals. At the same time, however, 

 the alga often grows considerably in size, the peripheric parts 

 uninterruptedly continuing their growth, developing short branches 

 more coalescing, w T hile the interior of the alga is filled with boring 

 mussels continually carrying on their destructive work. At last 

 there is frequently formed an opening in the part turning down- 

 wards. Then we have in hand a specimen inverted cup-shaped, 



