No. 3] REMARKS ON NORTHERN LITHOTHAMNIA. 89 



from a single locality, and I have also afterwards found sporangia 

 two- parted. I have above, when treating of L. tophiforme, men- 

 tioned the species in question and other crustformed species as 

 partly bearing sporangia two-parted as well as four-parted ones. 

 It might seem likely that each of these species should on that ac- 

 count have been divided into two distinct ones, as in the case of 

 some of the branching species. In the latter, however, as a general 

 rule only one kind of sporangia or the other is found, corresponding 

 to a certain distribution, whereas in the crustformed ones both 

 two-parted sporangia and four- parted ones rather often occur in 

 the same specimen, and sometimes in the same conceptacle. In 

 Ph. compactum I have even seen sporangia two-parted, three- 

 parted and four-parted in the same conceptacle both in specimens 

 from Norway and from America, the first-named ones in prepon- 

 derating majority. The same is the case with specimens from 

 Greenland. Cp. Rosenvinge 1. c. fig. 3. Besides I have, in 

 typical L. foecundum, seen two-parted sporangia and four-parted 

 ones in specimens both from Norway and from Ellesmereland. I, 

 therefore, at present do not venture to consider this state of things 

 otherwise than partly an abnormal development of the said organs, 

 partly they have probably not been fully developed. This is, 

 however, in many cases hardly or even impossibly decidable. 



As remarked by Professor Kj ell man 1. c, the alga forms a 

 crust almost circular, when developed freely on a plane substratum. 

 The surface is even and faintly shining. When several crusts are 

 formed on the same substratum and finally get confluent, the limit 

 of each of them may be more or less visible and sometimes be 

 formed by raised ridges. When growing older, the alga mostly 

 becomes more or less uneven, partly as a consequence of the form 

 of the substratum, partly by irregular effacing of the scars after 

 emptied conceptacles. New crusts are often developed one above 

 the other in a rather irregular manner, or sometimes small crusts 

 circular and almost disc-shaped occur upon old ones, representing 

 independent individuals. An uneven surface, however, particularly 

 rises from growing over and covering up small extraneous objects, 

 sometimes forming small angular excrescences like similar ones in 



