KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND. 20. N:0 5. 95 



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 deåned 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, lig. 7). The surface cells are isodiametric in 

 the tangential direction, with rounded cell-rooms, 5 — 7 ,«. in diameter. The thickness 

 of the wall amounts to 2 — 4 ,". (pl. 3, fig. 10). 



Organs of propagation. In this species I have seen only conceptacles of sporangia. 

 These are very numerous, disseminated both över the processes in their whole length 

 and on the crust between them without apparent order. They are small, 250 — 300 ,u. 

 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 elongated- 

 pyriform, sometimes slenderlj' spindleshaped-cylindrical, sometimes almost perfectly cy- 

 lindrical. Some of those measured by me, were 80 — 90 fi. long, 60 in. thick, others 

 about 120 ,«. long, 40 u. thick, again others 135—140 in. 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 L. calcareuni, being induced thereto by Har- 

 vey's description of Melobesia calcarea in Phyc. Brit. agreeing in certain respects with 

 the specimens I brought home from Spitzbergen. Kleen having seen these and having 

 found a form of Lithothamnion occurrino- in Nordlandcn to be identical with the form 

 from Spitzbergen, followed my example and recorded this plant under the name of 

 L. calcareum. 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 Corallinea^ recorded the plant under this name, and thus I 

 was prevailed upon not to abandon my former view in my subsequent work on the 

 alga3 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 



