No. 3] REMARKS ON NORTHERN LITHOTHAMNIA. 41 



which is then, by continued destruction, becoming more or less 

 convex- concave. Such a specimen represents f. obcrateriformis, 

 which is properly a forma siibsphcerica changed by attacks of ani- 

 mals. Cp. Norw. Lithoth. pi. 11. The part turning downwards 

 shows truncate, worn ends of branches more or less coalescing. 

 Cp. Contrib. II, pi. 2. The form may also become wreathlike. Cp. 

 Norw. Lithoth. pi. 12, fig. 2. Under certain circumstances the f. 

 ob crater if or mis may again almost assume its original shape. Cp. 

 above pag. 6 — 7. Also of f. ob crater if or mis there are found a 

 southern form with thinner branches (L. clehiscens in Norw. Lithoth.) 

 and a northern one with thicker branches (L. fornicatum 1. a). 



The form tuberculata seems partly to represent an old f. 

 obcrateriformis, whose upper branches have been in part worn 

 away by the friction of the water, whereupon shorter and thinner 

 branches have been developed over or round the worn surfaces? 

 forming short branches with wartlike processes or small bundles. 

 In places where the tidals are running very strongly, the bundles 

 are crowded and are often also gradually worn or partly torn 

 away, sometimes even getting an almost truncate appearance. 

 Cp. above p. 7—8 and Norw. Lithoth. p. 46, pi. 13. If new* 

 branches are developed in the part turning downwards, they often 

 do not form bundles, but are, however, thinner than in specimens 

 typically developed. 



The conceptacles of sporangia in this species are convex, 

 but little prominent or subprominent, 300(250) — 450 jj- in diameter, 

 often crowded below the apex of the branches. The roof is 

 intersected with 40 — 70 muciferous canals. The sporangia are 

 tetrasporic, 100 — 180 fi long and 40 — 80 jx broad. The con- 

 ceptacles of cystocarps are conical or subcorneal, of about the 

 same size as those of sporangia, and those of antheridia are also 

 concial and 200 - 250 (i in diameter. Old specimens, or specimens 

 much attacked by animals, are almost always sterile. Overgrown con- 

 ceptacles are now and then found in the peripheric parts of a branch. 



As to the synonomy, it is to be observed that L. delapsum 

 f. conglutinata probably belongs to f. obcrateriformis, though I 

 have not found ripe sporangia in it. 



