163 



growth get fully confluent, so that especially when older it looks 

 as if it had been a solitåry crust from the beginning. The crust 

 is at first fastened closely to the substratum, and often even in a 

 more advanced stage, but when older it most frequently is råtner 

 easily separated. It attains a thickness of 1.5 mm., frequently 

 about 1 mm. The central part is commonly a little thicker than 

 the peripherical, but the latter on the other hand less decreasing 

 than in the nearly allied L. circumscriptum, and the margin shal- 

 lowly crenate with more or less rounded lobes. The surface nearly 

 always is more or less uneven. Pl. 19, fig. 15 — 20. This uneven- 

 ness is partly caused by that of the substratum, partly b}^ cove- 

 ring up small extraneous objects but most often also by small 

 and irregular excrescences, and besides also by an irregular effa- 

 cing of the deep scars after the emptied and irregularly scattered 

 or here and there crowded conceptacles of sporangia. The surface 

 is also provided with numerous radiating and concentric striæ. It 

 is feebly wine-coloured, frequently lighter than in L. circumscrip- 

 tum, råtner dull or faintly shining, but gets darker and often rather 

 violaceous when dry. I have never seen new crusts formed upon 

 the primary. 



The lower, co-axil system is more vigorously developed than 

 in L. circumscriptum. The upper thickening layer is composed 

 of cells which are seen on a radial section to be arranged in rather 

 straight and well-marked rows, the upper ones more loosely united, 

 so that they alter decalcifying are rather easily separated by pres- 

 sure. The cells of these layers are up to l 1 /^ times the diameter 

 in length, or about 7—8 fi long and 5—6 fi thick. 



The concsptacles of sporangia, the only reproductive organs 

 hitherto known, are partly scattered partly densely crowded here 

 and there in the frond, even close to the periphery, as in L. com- 

 pactum, and not forming a sharply defined zone as in L. circum- 

 scriptum. They are at first seen from the surface of the frond 

 as slightly depressed-circular points about 80 — 100 <j. l n diameter. 

 Later these points get by and by decorticated and then forming 

 rather shallow holes frequently with not sharply marked edges, 

 the bottom of which forms a part of the roof, intersected with 



