65 



in such cases the conceptacles perhaps do not grow down. In 

 one specimen I found numerous small and disc-shaped, slightly 

 projecting, whitish and easily dissolvable processes which probably 

 are local formations that efface scars after emptied conceptacles, 

 but do not accord with similar formations that frequently occur in 

 this and other species, and I do not know whether they may have 

 been conceptacles of sporangia or cystocarps, probably, however, 

 the former. I have occasionally seen scars after filled conceptacles 

 on a section, overlapped by a new thickening layer of the frond. 



What I have named f. typica is represented in Contrib. 1. c. 

 pl. 2 (not the specimen under the same name on pl. 1) and is in 

 a full-grown stage easily recognized. But on the other hand it is 

 rather varying and assumes more or less irreguiar forms in its 

 struggle for existence, with more irreguiar and more anastomosing 

 branches bearing more numerous smaller and wart-like or occasio- 

 nally longer and branch-like processes, or even showing a tendency 

 to form smaller bundles. The branches frequently are 2.5 — 3 

 mm. thick. 



The form robusta perhaps ought to be considered a separate 

 species, but in the materials at my disposal, with nearly all the 

 specimens sterile, I have not succeeded in drawing any true .limit. 

 Nor have I seen old specimens of this form, but in its development 

 at least it very nearly accords with f. typica, and the reproductive 

 organs appear to be similar in both, but the branches frequently 

 are much coarser, more regular, with smoother surface. 



Also this form is in general at first fastened to shells, forming 

 a very thin crust, which soon produces densely crowded protu- 

 berances growing out into short branches divided in a subdichoto- 

 mous manner. By and by it completely surrounds the object and 

 becomes subspherical or hemispherical, attaining a diameter of about 

 15 cm., at length loosening itself and lies free on the bottom. The 

 crust always is thin, never, so far as I have seen, increasing in 

 thickness, but on the contrary by and by disappearing. The plant 

 has, like the typical form, a tendency to get hollow and opening 

 itself in the part turning towards the bottom, which, however, ap- 

 parently is advanced by attack by boring-muscles entering the central 



