KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND. 20. N:0 5. Se) 
marked limit into a more or less mighty layer of tissue whose cells arrange themselves 
in rows more and more radially, and while maintaining their multangular periphery, 
extend themselves in the radial direction, the walls getting thinner. Beyond this layer 
there is a greater or smaller number of layers less sharply defined from one another, 
formed of transversely square or rectangular cells arranged in pretty regular lines ra- 
dial as well as concentric. When the cells are rectangular, their longitudinal axis is 
often at right angles to the radius (pl. 3, fig. 7). The surface cells are isodiametric in 
the tangential direction, with rounded cell-rooms, 5—7 «w. in diameter. The thickness 
of the wall amounts to 2—4 uw. (pl. 3, fig. 10). 
Organs of propagation. In this species I have seen only conceptacles of sporangia. 
These are very numerous, disseminated both over the processes in their whole length 
and on the crust between them without apparent order. They are small, 250—300 uw. 
in diameter, slightly elevated above the surface of the frond, with convex roof; fig. 4, 
pl. 3. The gelatiniferous canals of the roof, in cross section, are 5—6-angular, 7—10 
“. in diameter. Their orificial cells differ scarcely or not at all from the adjoining 
surface cells (fig. 11, pl. 3). 
The sporangia are bisporic. This statement is founded on an examination of 
specimens from widely distant parts of the Arctic Sea. I have never, amongst the 
pretty numerous sporangia I have examined, found any containing more than 2 spores. 
As to shape and size they vary within wide limits. They are often pyriform or clongated- 
pyriform, sometimes slenderly spindleshaped-cylindrical, sometimes almost perfectly cy- 
lindrical. Some of those measured by me, were 80—90 uw. long, 60 «. thick, others 
about 120 uw. long, 40 w. thick, again others 135140 uw. long, 50—60 «. thick a. s. o. 
(fig. 12, 13, 14, pl. 3). 
Remark on the synonomy. When I mentioned this species from the Arctic Sea 
for the first time, I gave it the name of LZ. calcarewm, being induced thereto by Har- 
veys description of Melobesia calcarea in Phyec. Brit. agreeing in certain respects with 
the specimens I brought home from Spitzbergen. Ktrrn having seen these and having 
found a form of Lithothamnion occurring in Nordlanden to be identical with the form 
from Spitzbergen, followed my example and recorded this plant under the name of 
L. caleareum. Finding, however, on closer examination that the form from Spitzbergen 
could not be the English Melobesia calcarea and looking round for some known species 
with which the arctic form might be identified, it seemed to me that it might be re- 
ferred to L. fasciculatum, under which name I adopted it in Spets. Thall. 1. I had 
then only little opportunity to occupy myself with the genus of Lithothamnia, imper- 
fectly known at that time and very feebly represented in collections. Above all, I 
did not know in what degree these forms vary and what importance should be attached 
to external differences. All this made me unwilling to set down the plant from Spitz- 
bergen as a separate species. In a treatise published shortly afterwards, J. E. ARESCHOUG, 
the monographer of the Corallinew, recorded the plant under this name, and thus I 
‘was prevailed upon not to abandon my former view in my subsequent work on the 
alow of the Murman Sea. Having since then had the opportunity of studying the arctic 
as well as the Scandinavian forms of this genus longer and more closely, and having 
