and firmly adherent to the substratum. But on an irregular substratum it forms more or less 

 uni md irregular crusts, which little by little become continent, and sometimes at length 



look as it' developing small excrescences. There are two specimens from stat. 240, one of 

 which i-- attached to an irregular substratum, apparently some volcanic mass. The crusts of 



this specimen an- verv irregular, partly with small excrescences which are, however, owing to 

 the uneven substratum or to the covering up extraneous objects or dead crusts of the same 

 species. The other specimen is quite different in habit from a typically developed specimen, 

 formin» numerous and crowded wartlike excrescences or short branches about 1 mm. in 

 diameter. It has been attached to some rather loose and irregular object. Upon the primary 

 and at length anastomosed crusts, extraneous objects have attached themselves, and new crusts 

 have heen developed upon the latter. These crusts have been at least partly water worn, and 

 new crusts have again been developed together with another appearance of extraneous objects 

 in a rather irregular way, the crusts of the alga often converging and a little rising, and at 

 length more or less anastomosing, or covering up the said extraneous objects or roughnesses 

 of the subjacent parts. In this way the mentioned excrescences are formed. A vertical section 

 exhibits hvpothallic cells which are partly more elongated than frequently to be seen, sometimes 

 even forming a rather vigorous layer of tissue, though the hypothallium is in general slightly 

 developed in this species. The first mentioned specimen belongs without doubt to the species 

 in question, and also the other one is most probably a form of the same species, only peculiarly 

 developed owing to the substratum. 



In Lithoth. Adriat. Meer. I have mentioned that particularly Lithothamnion Philippii 

 develops partly a vigorous, partly a rather feeble hypothallic layer, depending on the shape 

 and nature of the substratum. The consistency is rather varying too, sometimes rather loose, 

 sometimes firmer than usually met with. A similar condition also appears in Lithothamnion 

 frutictilosum, GoniolitJion Foslici, Lithophyllum expansum and especially Lithopkyllum incrustans. 

 Under Lithophyllum oncodes I mentioned a specimen with comparatively loose consistency, — 

 firm consistency being the general character of the species. The species in question offers a 

 striking instance of a similar state of things. Thus pi. XI, fig. 2 represents a specimen covering 

 a piece of rather hard woocl. It is closely adherent to the substratum, although less firmly than 

 if the plant is attached to stones, as e. g. the specimens pictured pi. XI, fig. 1 and 3. However, 

 it does not difter in any essential degree from the latter ones, neither in habit, nor in consistency 

 and structure. On the other hand, the specimen pictured pi. XI, fig. 4 is rather differing in 

 both the latter respects, particularly, however, as to consistency, and in habit it shows a 

 more regular outline than usual. It is attached to a piece of very loose wood, i. e. mangrove 

 ( 'Rhizophora) \ forming almost circular and thin crusts which are somewhat bleached. The con- 

 sistency is looser, if not much looser, than specimens developed on a hard substratum. Besides, 

 in a vertical section of a crusts, the hypothallic cells are in part larger than usual in this species, 

 but not el( mgated or less elongated than e. g. ihose in the specimens above mentioned from 

 stat. 240. They often form almost rhizoid-like sinuosities or clustered crenules towards the 

 substratum. The perithallic cells are. however, of about the same size and shape as in the 

 typical form, although sometimes a little larger and oftener faintlv elongated in vertical direction, 



