50 M. FOSLIE. [1905 



— only an occasional variation, and is no true variety in the 

 usual sense. 



The species, as a general rule, is developed freely on the 

 bottom. But in certain circumstances it will, like several other 

 species, develop crust-like formations or attach itself to hard ob- 

 jects. In the latter case, it even develops a feeble crust, which 

 is, however, sometimes fairly extended, and which, at an early 

 stage of development, sends forth branches at first rather spreading, 

 but gradually growing approximate. This seems, however, to occur 

 much more rarely than in L. tophiforme. 



The conceptacles of sporangia in this species are partly scat- 

 tered, partly — and more frequently — densely crowded, parti- 

 cularly in the upper part of the branches, often so densely crowded 

 as to make the roofs angular. They are convex, partly but little 

 prominent, partly — and most frequently — subprominent, finally 

 almost superficial, 300 — 500 p. in diameter. The roof is intersected 

 with 50—80 muciferous canals. The sporangia are tetrasporic, 

 100 — 180 /J. long and 50—80 fi broad. The cystocarpic concep- 

 tacles, which generally occur in other individuals than those of 

 sporangia, appear scattered and are conical, 400 - 600 //. in dia- 

 meter. Those of antheridia are of the same shape as the latter, 

 and of about half the size in diameter. I have not seen overgrown 

 conceptacles of sporangia in this species, but the scars after con- 

 ceptacles emptied and but little prominent are sometimes effaced 

 by local formations of tissue, and are visible in a section. 



Like most other species, also L. soriferum prefers places where 

 the tidals are running strongly. It is found in a depth of 5 — 20, 

 and particularly 10 — 15 fathoms. In some localities it is wholly 

 or partly covered by Phymatolithon investiens and Litliothamnion 

 flavescens. It bears reproductive organs in the months of June — 

 September. 



The area of distribution is rather limited. In this respect the 

 alga stands in the same relation to L. tophiforme as L. inter- 

 medium does to L. glaciale. Nor does it occur in large numbers, 

 though here and there it is forming small banks. Of the forms 

 recorded f. squarrosa appears to be the most frequent one, whereas 



