33 



of f. americana, but they are on the whole less regular. There is similarity also as reoards 



the perithallic cells, though those of f. haingsisiana sometimes show a little thicker walls than 



those of f. americana, of which on the other hand only a single 



specimen has been examined (Fig. 1 7). In the above mentioned speci- 



mens from stat. 240 the structure partly fully resembles typical f. 



haingsisiana, partly the medullary hypothallium shows mostly a little 



shorter cells with corners partially rounded and thicker walls. Besides |§ 



the perithallic layer is more vigorously developed, frequently with a 1| 



little smaller and more thick-walled cells than in typical specimens. 



In these specimens a new hypothallium often stretches itself partially 



over the branches and covers roughnesses or extraneous objects. Such 



is also the case with the above mentioned specimens from stat. 93 



and 149. These specimens of the plant somewhat differing and more 



or less stunted come ver}- near to f. madagascarensis ] ), especially in 



structure. I have however seen but a single specimen of the latter 



from Madagascar, and besides a few quite young ones from the Pacific 



coast of Japan, which seem to belong to the same form. It may be 



that f. madagascarensis represents an independent species, but this 



cannot at present be decided. 



The conceptacles of sporangia in i. americana are somewhat 

 prominent and rather crowded in the upper part of the branches, 

 300 — 400 ij., in diameter, when seen from above. The roof is often '• ' ' A - Web - et FosL 



Part of a median section of a 



rather nattened in the central parts and here traversed by about 20 branch; x 72. 



muciferous canals. In f. haingsisiana they are of about the same size 



and more or less prominent, exceptionally however up to 450 u.. in diameter. The conceptacles 

 at length become overgrown by new-formed tissue, but such ones are not commonly seen in 

 the specimens examined, and they are in most cases peripherical. The sporangia are four-parted, 

 about 90 p.. long and 50 u.. broad. 



The very greatest number of the specimens collected are sterile. It seems to be the 

 same case with this species as with several northern or arctic ones that reproductive organs 

 are as a rule no more developed in old specimens, but mostly to be found only in somewhat 

 younger specimens. - - On the other hand, the said organs are to be found even in quite young 

 specimens of certain species, especially crustlike ones. The form haingsisiana is scantily furnished 

 with sporangia in the months of February, June, August and November, and f. subflabellata 

 in the month of November. 



The species in question seems to be most closely allied to Lithothamnion Dickiei, the 

 species last mentioned. It resembles a little certain forms of Lithothamnion falsellum in habit, 

 but is quite different in structure. It also recalls the northern species Lithothamnion dimorphum. 

 On the other hand it comes very near to Goniolithon frutescens f. congesia in habit. Cp. pi. III, 



Fig. 17. 

 Lithothcnnnion crubescens Fosl. 



ij M. Foslie. New Forms of Lithothamnia. — Det Kgl. Norske Vidensk. Selsk. Skiifter, 1901, X". 3. Tïondhjem 1901, p. 3. 



