20 M. FOSLIE. [1905 



long and 7 — 14 fi broad, their length being twice to four times, 

 usually twice to three times their breadth. The perithallic cells are 

 squarish, 8 — 11 fi in diameter, or vertically elongated, up to 15// 

 long and 12 or exceptionally 14 /* broad. 



The conceptacles of sporangia are depressed-hemispherical, 

 sometimes almost disc-shaped, 400 —800 fi in diameter, frequently 

 500—650 fi, and the roof intersected with 80—110 muciferous 

 canals. The sporangia are four-parted, 190 300 fi long and 

 50 — 120 /abroad. The said conceptacles finally become overgrown 

 in specimens typically developed and not too young, but in others 

 the roof falls into decay as in Lithoth. Iceve, and the scar is effaced 

 by new formed tissue. The conceptacles of cystocarps are conical, 

 500—600 or up to 800 fi, and those of antheridia 250 — 350 fi 

 in diameter. 



As remarked above under L. Iceve, it is rather uncertain 

 whether that species and L. fiavescens are specifically distinct. 

 Young and even fertile specimens seem almost undistinguishable, 

 apart from the substratum. However, in L, -fiavescens the crust 

 becomes thicker than ever seen in L. Iceve, the structure seems 

 to be slightly coarser in the former, the conceptacles of sporangia 

 frequently are a little smaller and finally become overgrown. On 

 the other hand the species in question approaches in habit young 

 specimens of Phymatolithon investiens, by which in certain loca- 

 lities it becomes partly covered. 



This species occurs in the sublitoral region and descends to 

 a depth of about 20 fathoms. It is attached to other calcareous 

 algae, particular^ Lithoth. glaciale and L. tophiforme, and some- 

 times also to shells of Balanidae. 1 ) Some specimens mentioned in 

 Norw. Lithoth. 1. c. as attached to stones can not be referred to 

 this species, although they are thicker than usual in L. Iceve. The 

 alga seems to prefer sheltered places. It appears rather scattered 

 and in small number of individuals. It has been found fructiferous 

 from June to the middle of September. 



r ) The form growing on shells of Balanidae with smaller conceptacles than 

 usual, I have denominated f. balanicola Fosl. herb.; but I do not admit it 

 here, as it seems to be too little differentiated. 



