256 KJELLMAN, THE ALG^ OF THE ARCTIC SEA. 



Bemark. Gobi's refusal to acknowledge as valid Areschoug's genus of Lithoderma 

 is apparently occasioned by his having misunderstood Areschoug's description of the 

 so called unilocular sporangia (cp. Bot. Zeit. 1877, p. 532). Fig. 6 in tab. 26 shows 

 these organs in the genus Lithoderma to differ most essentially in appearance, arrange- 

 ment, and origin from the same organs in the species of the genus Ralfsia. The differ- 

 ence is so essential that the alga in question cannot even, in accordance with the 

 modern principles of the systematic arrangement of the PhoeozoosporacecB, be referred 

 to the same family as the Ralfsice. It does not with regard to those organs agree with 

 the EncoeliecB, with which family Ralfsia must be placed, but rather with the Puncta- 

 riacece. It differs, however, so considerably from these in the morphological and ana- 

 tomical character of the frond, that it cannot be referred to that family either. The 

 genus Lithoderma is distinguished from all Phceozoosporacece proper that I know, by 

 the so called multilocular sporangia (gametangia) being arranged in specific stands 

 issuing from the surface-cells of the frond, and on this ground I have thought it best 

 to make as yet a separate family; (tab. 26, fig. 7). The structure and development 

 of the frond are also different in Lithoderma and Ralfsia. The former is in this respect 

 analogous to Melohesia, the latter to Lithojphyllum among the Corallinacece. 



Habitat. The present species is sublitoral, covering small stones on gravelly bottom 

 in 5 — 15 fathoms water. It usually occurs gregarious, characterizing the vegetation of 

 extensive areas. It is most often met with on exposed coasts. I have found it in the 

 Polar Sea with zoosporangia multilocularia (gametangia) during the latter part of September 

 and in December. 



Geogr. Distrih. It is probably circumpolar, though it is not known at present in 

 the American Arctic Sea. I have found it most abundant in the eastern part of the 

 Greenland Sea and in the Murman Sea. Its northernmost point is Treurenberg Bay 

 on the north coast of Spitzbergen Lat. N. 79° 56'. 



Localities: The Norwegian Polar Sea: Finmarken, local and scarce at Maas5 and 

 Gjesvaer. 



The Greenland Sea: common and rather plentiful on the coasts of Spitzbergen. 



The Murman Sea: common and abundant on the west coast of Novaya Zemlya 

 and Waygats. 



The White Sea: at Solowetzki Isles. 



The Kara Sea: pretty abundant at Uddebay. 



The Siberian Sea: Lat. N. 76° 8', Long. 0. 90° 25'; Irkaypi, Pitlekay, and the 

 Tshutsh-villages east of this point, at no place common or abundant. 



Baffin Bay: the west coast of Greenland, according to specimens collected by 

 Prof. Th. M. Fries. 



Lithoderma lignicola nob. 



L. thallo crustas elongatas, plus minus conflueutes formanle; filis verticalibus ex articulis 20 vel pluribus, 

 crassitudiue longioribus vel fequilongis contextis. Tab. 26, fig. 8 — 11. 



