No. 3] REMARKS ON NORTHERN LITHOTHAMNIA. 121 



on the shape and the quality of the substratum, and is mostly 

 composed of a few layers of cells, often only 2 or 3. Sometimes, 

 however, it can attain the same thickness as in f. macrocarpa or 

 up to about 350 ;j- with up to 8 layers of cells. Particularly in 

 Zostera and Thalassia the crust is, as a rule, very thin, and 

 often only 1 — 3 mm. in diameter, even if it bears conceptacles. 

 The conceptacles are then, for the most part, small and slightly 

 developed. Peculiarly in southern areas the form very often grows 

 "associated with Melobesia farinosa, and, a little more to the north, 

 with Melobesia Lejolisii. If it is not closely examined, it is easily 

 confounded with coarser forms particularly of the species last 

 mentioned. The conceptacles are also rather varying. They are 

 almost always largest in crusts vigorously developed. The tetra- 

 sporic sporangia are 80 — 130 p- long and 30 — 70 \j. broad. 



The form intermedia is a more northern form than the last 

 mentioned one. It is also much varying according to the quality 

 of the substratum and most nearly approaches the f. australis. It 

 is distinguished from the latter chiefly as to the shape of the con- 

 ceptacles, which are generally more conic. The form, therefore, 

 also nearly approaches the f. macrocarpa and is faintly defined 

 against the latter. In northern areas the form often grows asso- 

 ciated with Melobesia Lejolisii, and if it is not closely examined, 

 it is easily confounded with coarser forms of the said species. The 

 sporangia are bisporic, 60 — 120 /a long and 30 — 80 p- broad. 



The form macrocarpa, as a rule, develops thicker crusts than 

 any of the forms mentioned above, and it does not occur on so 

 heterogenous substrata as those forms. It is best developed on 

 algae of fairly firm consistency, e. g. Oigartina, Chondras, Asco- 

 phyllum. On Phyllophora it is rarely so vigorously developed as 

 on the said algse. It often encompasses branches of Furcellaria, 

 in part also of Ahnfeltia, on which also the two forms last men- 

 tioned are sometimes found. As remarked above, it approaches f. 

 intermedia, the crust only being thicker, the conceptacles larger 

 and often a little lower proportionately to the diameter. The bi- 

 sporic sporangia are 60—120 fx long and 30 — 60 \j. broad. 



The form Corallince I should be most inclined to put out as 



