en 
Rhododermis Crouan. 
Crouan in J. Agardh, Sp. Vol. II, pars 2, 1852, p. 504, 
1. Rhododermis elegans Crouan. 
Crouan in J. Agardh, Sp. Vol. II, pars 2, p. 505. Crouan, Florule de Finistère, 1867, p. 148, pl. 19, fig. 130, 
Batters, Mar. Alg. Berw., 1889, p. 91, pl. XI fig. 1 (forma polystromatica Batters). Kolderup Rosenvinge, 
Deux. mem., 1898, p. 18, id., Mar. Alg. N. E. Greenl. 1910, p. 104. 
This small arctic and north-atlantie species has been collected in several places 
in the Danish waters. It forms small, thin crusts of a lilac-rose colour with an 
irregular outline, the diameter of which scarcely exceeds 5 mm. It resembles in 
many respects Rh. parasitica of which Kuckuck has given an exhaustive description 
and splendid figures (Beitr. z. Kenntn. d. Meeresalg. 1. Wissensch. Meeresunters. N. F. 
II, Heft 1. 1897). According to Barrers, one of the principal differences is that 
the cells of the frond in Rh. elegans are broader than long, while in Rh. parasitica 
they are longer than broad. This difference is in reality general though not abso- 
lute, as may be judged from the figures of Kuckuck and from the fact that cells 
may be found in Rh. elegans, Which are at least as high as broad. Rh. parasitica 
differs further by its greater diameter, greater thickness and darker colour. A difference 
exists also in the structure of the border of the frond, this consisting in Rh. para- 
sitica of distinct filaments (Kuckuck, l. c. p. 7, Taf. VIII fig. 10) while it is continuous 
in Rh. elegans (fig. 118 A). 
The basal layer consists of radiating cell-rows, the cells of which are more or 
less lengthened in a radial direction. In the marginal part of the frond the cell- 
rows are frequently flabellately radiating towards the irregularly lobed border, here 
and there showing lateral ramifications (fig. 118 A). The cells are usually 5,5—7 » 
broad, 11/2 to 3 times as long as broad. In the basal layer lateral fusions between 
cells belonging to different cell-rows frequently occur, the cells corresponding through 
a broad open canal. Such fusions may occur at the very margin of the frond. 
More than two cells may sometimes fuse together (fig. 118 A, B). 
The crust is at first monostromatic, and a rather broad monostromatic mar- 
ginal part may often be found. The inner part of the frond was always found to 
be from 2 to at least 5 cells thick. I have never found it distromatic in a greater 
extent, and I must therefore suppose that it is only accidentally that Crovan has 
altributed a distromatic frond to this species, and that there is no reason to main- 
tain the var. polystromatica Batters. The cells contain several chromatophores as in 
R. parasitica. In the upper part of the crust the cells are 8—11y broad. In several 
specimens I found, projecting from the surface, scattered hyaline hairs (fig. 118 C). 
Their number varied; they were placed between the paraphyses or in the sterile 
parts of the crust. 
The sori form irregular spots on the surface of the frond; they consist of 
feebly curved paraphyses, usually 4- or 5-celled, 40—50 » long, at the base 5—9 4 
broad, and between them the sporangia, which are terminal on the vertical filaments 
of the crust, the upper cell of which has often the character of an upward slightly 
