238 
cells, as the occurrence and frequency of these cells seems to depend to a great 
extent upon external conditions. I therefore attach but little importance to the fact 
that such have not hitherto been found in two of the species mentioned below 
(M. minutula and microspora) as it must be considered highly probably that they 
will be found on further investigation of a greater number of specimens. More- 
over, hair-cells are found in M. Lejolisii, noted by Foszie under the genus Hetero- 
derma (see fig. 156). On the other hand, I could well imagine that it may later on 
be found justifiable to distinguish between those species in which the trichocytes 
are terminal in the horizontal cell filaments, as in M. farinosa, for instance, and the 
other, doubtless far more numerous species in which they are intercalary. Another 
vegetative character which might be thought to furnish grounds for generic distinc- 
tion, is the lack of- cortical cells shown below in the case of M. microspora. This 
point, however, still needs further investigation. As regards the cortical cells, it may 
also here be noted that in M. trichostoma, several of these were found above one 
another, cut off successively by the same frond cell. 
Where the frond consists of more than one cell-layer, there is often but slight 
difference between the basal layer (hypothallium) and the upright cell filaments 
proceeding therefrom (perithallium). Thus the walls forming the boundary belween 
these two tissues often lie at different heights, as for instance in M. microspora 
(figs. 176—179) and M. trichostoma (174—175). 
The number of spores in the sporangia is in most of the present species con- 
stant. In four species, 4 spores were found, in M. subplana a constant 2. In M. mt 
nutula only specimens with 4 spores were found, whereas FosrLıE gives 2, and in 
M. Fosliei some conceptacles were found with 4, others with 2 spores in the spor- 
angia. — À small stalk-cell under the sporangium was found in M. subplana. 
With regard to the antheridia, M. Lejolisii was found to differ from the other 
species in having the spermatangia formed at the end of long sterigmata, as first 
shown by Mrs. WEBER-van Bosse. In the other species, the spermatangia are elonga- 
ted cells, situate on the flat bottom of the antheridia-conceptacles. The orifice of 
the antheridia-conceptacles was in four of the present species often found drawn 
out into a spout, as first shown by Mrs. Weber-van Bosse in the case of M. Lejolisii. 
This is, however, not a constant character, as it may frequenily be lacking in all 
the species concerned. 
The carpospores are in all the cases investigated formed only in the periphery 
of the conceptacle, at the margin of the flat disc-cell. 
1. Melobesia Lejolisii Rosanoff. 
Rosanoff, Rech. anat., 1866, p. 62, pl. I fig. 1—13, pl. VII fig. 9—11; Areschoug, Observ. phycolog. Part. 
III, 1875, p. 3; Hauck, Meeresalg., p. 264; A. Weber-van Bosse, Bijdrage tot de Algenflora van Neder- 
land, Nederl. kruidk. archief. 2. Ser. 4. deel 4e stuk, Nijmegen 1886, p. 365; ead. in Hauck et Richter, 
Phykotheka univers. No. 163; Foslie, Remarks, 1905 (1906) p. 102 (f. typica); Mme P. Lemoine, Struct., 
p- 180, fig. 103; ead., Calcareous Algæ in Report on the Danish Oceanogr. Exped. 1908—10 to the 
Mediterranean etc. Vol. II, 1915, p. 19. 
