49 



to but seldom encompassing smaller stones. However, growing 

 niore scattered, or in the periphery of a greater bank it often 

 fastens itself, apparently in a somewhat advanced stage of develop- 

 ment, to smaller stones, but later again it appears to loosen itself 

 from the stone. Pl. 5, flg. 4. Occasionally different individuals 

 become confluent. Pl. 5, fig. 3. ln shallow sounds with rapid 

 tides the frond often gets rather compressed, forming subhemis- 

 pherical masses, that attain a diameter of 12 cm., more commonly, 

 however, globose or subglobose and about 8 cm. in diameter, or 

 less. The branches are short, generally shorter than in f. typica, 

 very densely crowded, straight and level-topped, and towards the 

 apex nearly always carrying short and wart4ike processes. It is 

 much anastomosing especially in the central portion and here now 

 and then forming lobes, however, the anastomose frequently ex- 

 tending pretty far upwards, and here and there even nearly to the 

 tip of the branches. The ends are as a rule obtuse or almost 

 truncate; but particularly if being under the influence of rapid tides 

 they become quite truncate in the part turning upwards, or also 

 in the part turning towards the bottom, but, so far as I have seen, 

 more seldom only in the last named part, and sometimes nearly 

 disc-shaped. Under such conditions the upper part of the branches 

 occasionally gets denudated, as in the typical form, however, appa- 

 rently more seldom than in the latter. The plant frequently is 

 much attacked chiefiy by boring-muscles, and, as is common at 

 least in nearly all the northern Lithothamnia, intersected with 

 numerous passages made by worms, occasionally leaving only a 

 thin peripherical portion; or a part of the plant, or even the whole 

 plant collapses. Pl. 5, fig. 4. 



I have not been able to draw any limit at all between the 

 plant that Kjellman 1. c. describes under the name of L. inter- 

 medium and the present species, and I, therefore, consider it a 

 form of this species. Specimens determined by Kjellman himself 

 show transitions especially to the typical form of L. fruticulosum, 

 and, as I apprehend Kjellmans description of his plant, it in part 

 includes the named form. Thus fig. 1 on pl. 4 1. c. can scarcely 

 be separated from L. fruticulosum f. typica in the sense the latter 



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