Contribution. I. 57 



passes gradually into D. amplissimum f. typica, which has 

 squarish or vertically rectangular cells by a thickness usu- 

 ally varying between 50 and 60 \i, sometimes a little thicker, 

 sometimes thinner. In H a u c k et R, i c h t. Phyk. univ. Nr. 

 8 such an ' intermediate form is distributed by Collins 

 under the name of PorpJiyra miniata. It has the outward 

 appearance of D. amplissimum f. typica but it is, at the 

 middle part of the frond, only 36 \l thick, and the cells are, 

 in cross section, horizontally rectangular, resembling fig. 18 

 by Strom felt 1. c. Another specimen from Nahant, Mass.,' 

 communicated to me by Collins, coincides almost fully 

 with the typical form of D. tenuissimum. The frond is at 

 the middle 25 p. thick. I therefore think D. tenuissimum 

 ought to be regarded as a form of D. amplissimum. 



The typical form of D amplissimum is distinguishing 

 itself by its darker colour, greater thickness and especially 

 by its being densely folded, « often so deeply that the folds 

 extend to the middle line of the frond*. However from this 

 deep folding it passes gradually into quite smooth, and then 

 it approaches much to D. miniatum (Lyngb.). 1 Such a form 



*. I have only seen a single specimen of D. miniatum, which I -found 

 some years ago at Gjesvaer in "West-Finmarken, attached to the rudder 

 of a smaller vessel then carrying trade between Gjesvser and Ham 

 merfest. I suppose this vessel the preceding year has been in the 

 neighbourhood of Spitzbergen, and there the spore has fastened itself 

 to the rudder, because the species has not been found earlier nor late 

 at the coast of Norway. I have not succeeded in getting accurate 

 informations as to the route of the vessel that year. 



The specimen in question accords well with the description given 

 by Lyngbye in Ilydr. Dan. t. 29, and the figures by K ii t z i n g in 

 Tab. Phyc. 19, t, 81, and Kj ell man in N. Ish. Algfl. t. 18, fig. 9. 

 The margin is irregularly lacinia^e and somewhat denticulate, and the 

 middle of the frond has a thickness of 72 ]X. The specimen was col- 

 lected in the beginning of September, bearing sporocarps and antheri- 

 dia. Thus this plant is not always dioecious. Cp. Kj ellm, N, Ish, 

 Algfl. p. 238. 



