259 
The crust is generally orbicular, scarcely exceeding 2 cm in diameter. In one 
locality only I found larger crusts expanded over stones; as these crusts also in 
other respects differred from the others, they will be mentioned separately below. 
The crusts are 1 to 1,5 mm thick. 
According to FosLie, the hypothallic layer mainly resembles that of Lithoth. 
lœve, being rather feebly developed (Remarks p. 112). I found it, however, always 
consisting of one layer only, the upright filaments springing out from it in a vertical 
or nearly vertical direction. The thickness of the perithallic cells varies between 6 and 
9; the height 
is generally Se oo 
greater than the : g 5 
breadth, often 
about double 
SD) = 
(about 134), but KANN 
2 OL WZ 
it may be of ORI 
the same size or OXY 2 £6 MOK) 
even smaller. \ AL G ( 
FosLie descri- OO ¢ Ole 
bes these cells 
as squarish; I 
found them ge- 
nerally more or 
less roundish, 
frequently ap- 
proaching the 
ellipsoid or 
globe. They are Fig 180 
connected with Lithophyllum orbiculatum. A, vertical secant of erase: B, under part of the same crust. C, 
the cells of the horizontal section of crust showing the tranverse pits. D, vertical section of margin of frond. 
E and F, vertical sections of aberrant specimen (no. 5341), F, showing the hypothallium. 350 : 1. 
neighbouring fil- 
aments through transversal pits situated about in the middle of the cells; in trans- 
verse sections 3 to 5 such pits are seen in each cell (fig. 180 C). The crust is 
traversed by horizontal limiting lines which are stained intensely blue by hæm- 
atoxyline; they are often seen crossing the middle of the cells (fig. 180 A). Mme 
Lemoine did not find such limiting lines in any species of Lithophyllum (Struct. 
p. 28). The cells of the perithallium are frequently filled with starch grains, par- 
ticularly in the under part of the crust. The surface of the frond is frequently 
much inclined towards the border, which in vertical section shows a great marginal 
cell (fig. 180 D). 
The conceptacles of sporangia are completely immersed; they had in the spe- 
cimens examined a transverse inner diameter of 92—116 ~; they are generally almost 
globular in a vertical section. They haye a single pore in the middle of the roof 
37% 
bp} 
