M. FOSLIE. 



[1909 



Archæolitliothamnion marmoreum (Mun.-Chalm.) Fosl. mscr. 



Lithothamnion marmoreum Mun.-Chalm. (1876) sec. spee. herb. Bornet; Wright, 

 Proc. Dubl. micr. Club 1880 p. 1 1 ; De Toni, Syll. Alg. IV p. 1763. 



In the slide of this species the alga forms fragments in the 

 calcareous mass of irregular roundish form, about 3 — 4 mm. in 

 diameter. There is no distinct disjunction of hypothallium and 

 perithallium. The cells are partly subsquare, 9 (7) — 14 p. in dia- 

 meter, partly and oftener vertically elongated, 11 — 22 (25) p. long 

 and 9 — 14 ji broad, here and there in the outermost part of the 

 perithallium horizontally elongated, 6—9 by 9—12 //-. The cavi- 

 ties of sporangia overgrown are densely crowded, separated from 

 one another by cells much elongated, diverging from the normal 

 cells and forming long curved rows according to the form of the 

 cellular layers. They are 54 — 76 fi long and 29 — 40 [J. broad. 



The species, on one side, seems to approach A. nummiditi- 

 cum (Giimb.) Fosl, " but is, on the other hand, probably more 

 nearly related to A. Aschersonii (Schw.) Fosl. It is distinguished 

 from the latter by longer cells. 



Lithophyllu7n(?) helgicum Fosl. mscr. 



In the handpiece mentioned this species forms terete, partly 

 somewhat knobby, whitish fragments of branches. They are 2 — 9 

 mm. long and 1 — 2 or mostly about 1.5 mm. thick. They occur 

 in large numbers and constitute about three fourths of the whole 

 mass. In this respect the alga seems to appear in almost the 

 same way as Lithothamnion parisiense Giimb. NuUip, p. 42. In 

 a longitudinal section a medullary hypothallium forms the essential 

 part of the thickness of the branch. The two sections mentioned, 

 however, have not hit the longitudinal axis, but have fallen some- 

 what obliquely to it. Therefore, I cannot state certain measures 

 of the hyphothailic cells. They do not form well-defined cup- 

 shaped layers of tissue, as in the branched forms of the genus 

 LitJiothamnio7i, but are without any fixed order. The cells are 

 about 25 — 50 jj. long and 11 — 16 (18) p- broad, with the longi- 

 tudinal walls more or less curved. The former measures, however, 

 are very uncertain, as in most cases, particuiary in the central 



