18 M. FOSLIE. [1905 



however, considerably thinner, the conceptacles frequently larger, 

 more superficial and never becoming overgrown as in the said 

 species. 



I omit the two forms of this species (f. macrospora and f. 

 tenuissima) formerly admitted, as a fair line cannot be drawn. 

 The thickness of the crust and the size of the conceptacles, indeed, 

 prove much varying even in one and the same species. 



The shape and the size of the cells in the species in question 

 have not earlier been stated. The structure, otherwise, shows the 

 same uniformity as in several other species, and considerable mutual 

 resemblance to that of several northern ones. Nor can I state a 

 sure average measure, having in this respect only examined a 

 couple of young specimens. The hypothallic layer mostly seems 

 to be rather faintly developed. The length of the cells is double- 

 or thrice, now and then even four times the breadth, the length 

 being 15 — 35 ;x and the breadth being 6—11 jx. The perithallic 

 layer is composed of cells which are squarish, abouth 7 fx in dia- 

 meter, or vertically elongated and up to 12 [x long and 11 \x broad. 

 In crusts proportionally thick this layer shows an indistinct strati- 

 fication. Cp. Rosenv. Gronl. Havalg. 1. c. fig. 4 — 6. 



The conceptacles of sporangia are depressed hemispherical or 

 almost disc-shaped, most frequently superficial or nearly so, 0.5 

 (0.4) - 1 mm. in diameter, frequently 0.6—0.8 mm., and the roof 

 is intersected with 80 — 120 muciferous canals. The said concep- 

 tacles are generally numerous and rather crowded, some of them 

 here and there so densely crowded that the roofs become angular. 

 The sporangia are four-parted, 200—600 ti long and 100 — 200 [t. 

 broad. But the alga sometimes also seems to bear two-parted 

 sporangia. Cp. Stromfelt 1. c, Rosenvinge 1. c, Norw. Lithoth. 

 p. 146 and below under L. toph i forme. The conceptacles of cysto- 

 carps are conical, frequently 600—800 fx, and those of antheridia 

 of the same shape and about 350 fx in diameter. 



The species occurs rather numerously almost in all the areas 

 where it is dispersed. It is found only on hard ground and occurs 

 in preference in localities where the tidals run rather strongly, but 

 also both on the open shore and in sheltered places. The alga is 



