235 
cells of the basal layer situated at the periphery of the conceptacle lengthen in a 
vertical direction, fuse laterally two or three together, and are finally disorganized, 
the upper part of their membrane being 
dissolved as far as it meets the cavity of 
the conceptacle. The cells of the same 
layer forming the central part of the floor 
of the conceptacle are disorganized in the 
same Way, their contents finally disappearing, 
but they do not lengthen. In fig. 152 D the 
contents of these cells are still visible. In 
the sexual conceptacles the basal layer is Fig. 153. 
exhausted in a similar way. The formation Epilithon memb anaceum vertical, somewhat excentric 
RN 3 section of sporangial conceptacle. 345:1. 
of the three dividing walls of the sporangia 
is almost simultaneous, the walls advancing slowly from the periphery towards the 
longitudinal axis of the sporangium (fig. 152 B, D). 
The antheridial conceptacles were found agreeing with the description and 
figure of RosanorF (I. c. p. 59, pl. II fig. 14). The cells surrounding the orifice are 
elongated and directed obliquely upwards (fig. 154). The antheridia clothe the bottom 
of the conceptacle; their development and structure have been followed by GuIGNARD, 
who found that they are seriate in densely placed short filaments. When the sper- 
matia are to be formed, the protoplasm accumulates around the nucleus in the 
middle of the cell and becomes surrounded by a thin membrane, while the rest of 
the contents develop into two appendices, first described by Rosanorr and named 
“oreillettes”. 
The orifice of the cystocarpic conceptacles is clothed with similar elongated, 
hair-shaped cells like those of the antheridial conceptacles, but more numerous; 
ihey are directed inwards or downwards in the under part, upwards in the upper 
part of the orifice. The carpospores are only produced at the periphery of the 
conceptacle; in the central part of the floor carpogonia are still visible, when the 
carpospores are well developed (fig. 155 B). As to the structure of the procarps I 
cannot give any certain 
statement; they seem to 
resemble those of Litho- 
thamnion polymorphum. 
The species, referred 
by earlier authors to the 
genus Melobesia, had been 
transferred by HEYDRICH 
Fig. 154. in 1897 to a new genus 
Epilithon membranaceum, vertical section of antheridial conceptacle. 500:1. u a 
Epilithon, which was re- 
duced in the following year by FosLiE to a subgenus of Lithothamnion, with whith 
it agrees by the fructification. The want of differentiation in hypothallium and 
30* 
