104 



the typical form of the species. It even is partly included in the 

 form of L. colliculosum mentioned in Contrib. 1. c. However, 

 most of the specimens then gathered belong to the form that I 

 have named f. clensa. Others show transition to f. rosea, or being 

 most nearly related to this form, of which I have later collected 

 specimens that fully accord with British ones. 



The form densa is characterized by its frequently thin crust 

 which apparently seldom attains a thickness of 1.5 mm. It bears 

 numerous and densely crowded knobs up to 4 mm. high, frequently 

 about 2 mm., by a thickness of 1—2 mm. These knobs are cy- 

 lindrical or slightly tapering, or enlarged towards the tip, simple, 

 or now and then towards the apex provided with one or two 

 wart-like processes, frequently with obtuse apices. Pl. 17, fig. 8—10. 

 In a younger stage the edges of adjacent crusts stumbling each 

 other generally raise themselves against each other, forming more 

 or less elevated ridges. Cp. Contrib. II, pl. 3, flg. 1. These ridges 

 rather seldom are to be seen in fully developed or older individuals, 

 then being covered with knobs. The plant is often accompanied 

 by other species, especially L. Stromfeltii, which it, not seldom, 

 by and by covers, and is fastened to stones or occasionally shells, 

 Two specimens from Spitzbergen kindly communicated to me 

 by Conservator Sparre Schneider fully accord with Norwegian 

 specimens of this form. They are dredged between Amsterdam- 

 oerne and Norskoerne by Capt. Nils Johnsen of Tromso. 



A form apparently nearly. related to the latter is f. laxa, but 

 on the other hand I have been in doubt whether it might not per- 

 haps be regarded a separate species. I have seen only a solitary 

 specimen bearing a couple of not fully developed conceptacles of 

 sporangia, and this is an American specimen. Pl. 17, fig. IL 

 Collins' collection D., Rockport, Mass. However, I have Nor- 

 wegian specimens which closely resemble the latter in habit, but 

 they are sterile. This form rather differs in habit from f. densa, 

 and is characterized by its thicker crust, up to 3 mm., but appa- 

 rently somewhat varying in this respect, as parts of one and the 

 same specimen may be only 1 mm. in thickness, and now and 

 then a new crust partly is formed upon the primary. The crust 



