No. 3J REMARKS ON NORTHERN LITHOTHAMNIA. 63 



by boring mussels, and finally becoming convex-concave, such as 

 in L. fornicatum f. obcrateriformis, with the lower ends of the 

 branches truncate. A similar specimen is represented fig. 5, but 

 here new crustlike formations partly cover the worn lower ends 

 of branches, here and there with new branches being in develop- 

 ment. Fig. 6 shows a similar specimen with a lot of branches 

 new-developed, resembling those of the parts turning upwards of 

 the specimen, though often being more delicate than the latter. 

 Cp. fig. 1 — 3. Tn certain localities the peripheric parts of the alga 

 will be worn by friction in the same way as in L. Ungeri and 

 in several other species branching. I have seen specimens of f. 

 typica in which a large part, of the alga has been thus torn away, 

 only leaving the central parts consisting, as it were, of a network 

 coalescing, branching parties more or less incise or flattened. 



The form gracilescens on one side resembles small specimens 

 of f. typica, and on the other hand it runs into specimens of f. 

 saxatilis loosened from the substratum. 



The form saxatilis first forms a crust faintly developed, from 

 which very short branches are emitted, partly somewhat spreading, 

 partly and more frequently approximate, with wartlike processes 

 or side- branches more or less coalescing and forming small bundles. 

 It is often detached from the substratum and lies freely on the 

 bottom. This form partly embraces L. norvegicum f. saxatilis, 

 Norw. Lithoth. pi. 16, fig. 12-23 and Rev. Syst. Surv. Melob. 

 p. 13, i. e. specimens with tetrasporic sporangia. 



The conceptacles of sporangia in this species are usually 

 crowded in the upper part of the branches, convex, but little pro- 

 minent, or subprominent, finally often flattened, 300 (250) — 400 \i 

 in diameter. The roof is finally very thin and easily falling to 

 decay, traversed by about 50 muciferous canals. The sporangia 

 are four-parted, 110—180 fi long and 40—80 p broad. In f. 

 saxatilis the said conceptacles occasionally are gradually over- 

 grown. Those of cystocarps are conical, rather low, and about 

 500 fi in diameter. 



As to the synonymy, I still think it most likely that L. bys- 

 soides Unger from the neighbourhood of Bergen belongs to L. 



