62 M. FOSLIE. [1905 



17. Lithothamnion nodulosum Fosl. 



Norw. Lithoth. (1895), p. 116. 



f. typica. 



Lithothamnion nodulosum Fosl. 1. c. pi. 21, fig. 1 — 6, Rev. Syst. Surv. Melob. 

 (1900), p. 13. 



f. gracilescens Fosl. 



Rev. Syst. Surv. Melob. (1900), p. 13; Lithothamnion gracilescens Fosl. Norw. 

 Lithoth. (1895), p. 59, pi. 15, fig. 20—27. 



f. congregata Fosl. 



Rev. Syst. Surv. Melob. (1900), p. 13; Lithothamnion congregatum Fosl. 

 Norw. Lithoth. p. 114, pi. 20. 



f. saxatilis Fosl. mscr. 



Frond attached to small stones, afterwards often detached, 

 branches very short, more or less coalescing, about 1 ,5 mm. thick, 

 frequently forming small bundles rather approximate. 



Syn: Lithothamnion byssoides Unger, Leithakalk, p. 19, t. V, fig. 1 — 8. 

 Lithothamnion nodulosum De Toni, Syll. Alg. IV (1905), p. 1743. 



This species is developed in the same way as L. Ungeri, 

 and resembles the latter, but is more delicate. It is branching 

 from the centre of the frond, sometimes, attached to pebbles, deve- 

 loping a feeble crust. The branching is at first not very dense, 

 and the alga then bears in habit a striking resemblance to L. 

 norvegicum. When growing older, it becomes more densely 

 branching, and the branches, 1 — 1,5 mm. in diameter, develop a 

 larger or smaller number of wartlike processes or short side-branches 

 forming bundles more or less dense. This is particularly the case 

 in localities where the alga is attacked by boring mussels dissolving 

 the central parts. Cp. Norw. Lithoth. pi. 21, fig. 1—6. Gradually 

 the form is developed which I have denominated f. congregata. 

 Cp. 1. c. pi. 20. Especially in this form the outer branches are 

 frequently more straight than elsewhere, such as is the case with 

 certain forms of L. Ungeri. Like corresponding forms of other 

 species, it has risen from the alga being attacked by animals, and, 

 therefore, strictly speaking is no form independently developed, 

 though often very peculiar. Of the specimens figured 1. c. pi. 20, 

 fig. 4 represents the part turning downwards of a specimen having 

 originally been subspherical or depressed-spherical, then hollowed 



