No. 3] REMARKS ON NORTHERN LITHOTHAMNIA. 39 



(1S95), p. 54, pi. 15, fig. 1-8 (excl. f. connata, f. patula); De Toni, Syll. Alg. 

 IV (1905), p. 1735. 



f. obcrateriformis Fosl. mscr. 



Lithothamnion fornicatum f. typica Fosl. 1. c. ; Lithothamnion dehiscens f. 

 typica Fosl. 1. c. pi. 11, pi. 12, fig. 2. 



Frond finally convex-concave or sometimes subhemispherical. 

 f. iuberculata Fosl. 



Rev. Syst. Surv. Melob. (1900), p. 12; Lithothamnion dehiscens f. grandi'rons 

 Fosl. Norw. Lithoth. p. 45, pi. !3. 



f. robusta Fosl. 



Lithothamnion fornicatum f. robusta Fosl. Norw. Lithoth. p. 36, pi. 9. 



Syn: Apora polymorpha Gunn. in Act. Nidros. IV (1768), p. 71, partim, t. 

 XV, fig. 1. 



Lithothamnion fasciculatum Aresch. Obs. Phyc. 3 (1875), p. 5, partim! 



Lithothamnion delapsum f. abbrevita Fosl. Norw. Lithoth. p. 50? De Toni, 

 Syll. Alg. IV (1905), p. 1733? 



As I observed, in treating of L. intermedium Kjellm., I se- 

 parate from this species a form which was originally referred to 

 it both by the author who described the species and by myself in 

 Norw. Lithoth. The said form, repeatedly branching from the 

 centre of the frond or sometimes attached to small pebbles, deve- 

 loping a very feeble crust, is to be transferred to L. fornicatum. 

 It very nearly approaches L. TJngeri f. fastigiata, which, therefore, 

 also has to be transferred to the species in question. With the 

 limitation stated above, L. fornicatum represents a species much 

 varying in habit and hardly distinguishable from several other spe- 

 cies. This is particularly due to attacks of animals. Thus scar- 

 cely any other boreal-arctic calcareous alga is found more attached 

 by boring mussels than this one. 



The form subsphmrica seems to be the typical form of the 

 species. It is partly spherical, partly, and more frequently com- 

 pressed-spherical, which seems always to be the case in places 

 where the tidal waters run strongly. The form is branching from 

 the centre, the branches repeatedly subdichotomously divided, erect, 

 fastigiate and straight, either terete or subcylindrical or subcom- 

 pressed, towards the apex often carrying small wart-like processes, 

 rather anastomosing, with the ends rounded or obtuse. Cp. Norw. 



