10 M. FOSLIE. [1900 



surface of the frond, afterwards decorticated and at length forming 

 an almost point-like deepening, the bottom of which intersected 

 with a few muciferous canals; sporangia between early destructible 

 walls, through gelinated, at length loosening tips corresponding 

 with the muciferous canals in the roof. 



Conceptacles of cystocarps unknown. 1 ) 



Sect. I. Endobotroideæ Fosl. 



Conceptacles of sporangia growing down into the frond. 



1. Cl. compactum (Kjellm.) Fosl. 



f. typica. 



f. testacea Fosl. (L. testaceum Fosl. Norw. Lith.). 



2. Cl. loculosum (Kjellm.) Fosl. 



Sect. II. Epibotroideæ Fosl. 



Conceptacles of sporangia not growing down into the frond. 



3. Cl. circumscriptum (Stromf.) Fosl. (incl. L. dumm Kjellm.). 



f. typica. 



f. coalescens Fosl. (L. coalescens Fosl. Norw. Lith.). 



4. Cl. evanescens Fosl. 



Gen. Lithothamnion Phil emend. 



Conceptacles of sporangia soriform, superficial or subimmersed; 

 sporangia between partly enduring partly destructible walls, through 

 gelinated, at length loosening tips corresponding with muciferous 

 canals in the roof. 



1 ) It is as vet not quite certain whether this apparenth' well marked genus 

 is to be considered a separate one or a subgenus of PhymatolitJwn. The 

 conceptacles of sporangia have a great outward resemblance to those in 

 Eulithopliyttum, but the development of the sporangia accords in the 

 main with PJiymalolithon except as regards some diversities in the roof, 

 as well as the walls between the sporangia disappearing in an earlier stage 

 than in the latter. I have seen but a solitarv, stunted and not certain 

 specimen of Cl. circumscriptum only furnished with a couple of concep- 

 tacles of cystocarps in a rather j'oung stage. From this it seems as if 

 the genus approaches IAtJiophyttum, while on the other hand the sporangia 

 show a close relation to PhymatoMthon, which also in other respects 

 probabl}' in fact may be the case. 



