No. 3] REMARKS ON NORTHERN LITHOTHAMNIA. 65 



18. Lithothamnion tusterense Fosl. mscr. 



Frond freely developed at the bottom, subspherical, 4—6 cm. 

 in diameter, repeatedly subdichotomously branching ; branches being 

 issued in all directions from the centre, terete, about 1,5 mm. thick, 

 more or less curved and subfastigiate, often with numereous 

 wartlike, lateral processes or short lateral branches ; conceptacles 

 of sporangia subprominent, 300 (250) — 400 p- in diameter; spor- 

 angia bisporic, 90—300 f*. long, by 40 — 60 /*. . 



This species resembles in habit and in structure small speci- 

 mens of L. nodulosum, and is distinguished only for the partition 

 of the sporangia. Cp. Norw. Lithoth. pi. 21, fig. 3 — 6. A number 

 of specimens from the Altenfjord and from Lofoten on one side 

 rather resemble delicate forms of L. topkiforme f. divergens and 

 are very nearly approaching certain forms of L. Oranii, or even 

 L. norvegicum, and on the other hand coincide in habit with 

 young forms sparely branching of L. nodulosum and L. tusterense. 

 They are furnished with bisporic sporangia and, therefore, most 

 nearly connected with the latter species. However, as I have not 

 in these places seen true transitions to old and typical L. tusterense t 

 I do not venture at present to refer the said specimens to this 

 species. Specimens typically developed have hitherto been found 

 in small number in a single place fairly sheltered, here appearing 

 in a depth of 3 — 4 fathoms. The alga is sparingly furnished with 

 sporangia in the month of August. 



Area: Norway: Tusteren north of Kristiansund, N.(!). 



19. Lithothamnion norvegicum (Aresch.) Kjellm. 



N. Ish. Algfl. (1883), p. 122, pi. 5, fig. 9—10! Lithothamnion calcareum 

 var. norvegicum Aresch. Obs. Phyc. 3, p. 4 ! 



f. pusilla Fosl. 



Rev. Syst. Surv. Melob. (1900), p. 13; Lithothamnion coralloides f. norvegica 

 Fosl. Norw. Lithoth. (1895), p. 62, pi. 16, fig. 1—11. 



cilescens. However, they have partly been worn by friction and not typi- 

 cally developed. Therefore, the determination may admit of doubt. 



Besides a few specimens from Denmark (Aarhus Bugt), about 1 — 2 cm. 

 in diameter, considerably remind of a stunted L. nodulosum. But as they 

 occur together with typical L. norvegicum, they are likely to represent a 

 form of the latter species. 



