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organs, so that the convex conceptacles are cystocarpic ones in 

 development. There is a slight difference between the convex con- 

 ceptacles in the specimens from Mandal and the convex in those 

 from Helgoland, as the latter appear frequently to be even less 

 prominent and, especially those cup-shaped, in general a little larger 

 than the former, although I, on the other hand, have not seen 

 any true limit between the convex, in part decorticated, and the 

 cup-shaped and fully developed conceptacles. 



There can be but little doubt that the here mentioned speci- 

 mens belong to one and the same species, or to the present one. 



Also these conceptacles apparently grow down into the frond, 

 but are on the other hand often effaced by local formations of 

 tissue. In one specimen with all the conceptacles emptied I found 

 numerous such formations forming even disc-shaped, light and 

 slightly projecting processes, which I, however, have occasionally 

 seen also in other species. 



Remark on the synonomy. Most of the authors from the 

 former centuiy did not refer crust-like Lithothamnia to this species, 

 or all the forms known were apprehended as one and the same 

 species, L. polymorphum. Among these probably was Linne, 

 Gunner us, Esper, Ellis et Solan der, Mo hr, and others. 

 The latter refers 1. c. to Apora polymorpha Gunn. in Act. Nidros. 

 4, p. 70, which includes the forms mentioned under L. ooreale, L. 

 fruticulosum and L. coralloides, and he adds: „I Fioru-Maalet 

 traeffes den almindelig, men under en anden Skikkelse, nemlig ikke 

 anderledes end en kalk, der har beklsedt Stene, Snekker Dg Skaller, 

 oftest kurlakrod, uden Grene eller Knorter". Here probably is in- 

 cluded the present species, as well as L. circumscriptum and L. 

 Stromfeltii. Also in the former half of this century the species 

 often has been taken nearly in the same sense (cp. Johnston 

 and Kiitzing 1. o), or it has been very differently understood, 

 until Areshoug defined it as a true crust-like plant, but later, 

 and even by Areschoug himself, it has been the general practice 

 to refer all or nearly all such forms to the present species. Cp. 

 Kjellm. 1. c. 



Of L. purpureum Cr. I have seen 4 small fragments from 



