_181 
named species. The genus Cruoria, to which the species of LyNGByE was referred 
in 1835 by Fries, was also very ill defined. ARESCHOUG and the later authors, how- 
ever, have applied the name of LYNGBYE and Fries to the species here treated of, 
and it must be used in the future in the same sense, as the specific name of LYNGBYE 
in fact comprises both species. 
This species, in habit quite resembling Petrocelis Hennedyi, forms crusts on 
the stems of Laminaria hyperborea, stones, shells of Mytilus and barnacles, more 
rarely on Fucus serratus and 
the basal part of Halidrys 
siliquosa, from 1 to 12 cm in 
diameter or more. The crust 
has at first a basal layer con- 
sisting of one layer of cells 
from which the vertical fila- 
ments are given off. The fila- 
Fig. 100. Fig. 101. 
Cruoria pellita. A, border of frond seen from above. B, verlical ‘section Cruoria pellita. Basal layer of frond seen 
of under part af frond showing basal layer and sub-basal layer. C, simi- from the under face, showing creeping 
lar, older crust. A, B 390:1. C 230:1. rhizoidal filaments. 390:1. 
ments of the basal layer are radiating towards the margin (fig. 100 A). According 
to Scumitz and HAUPTFLEISCH (1897, p. 535) the thallus is quite coalesced with the 
substratum and without root-hairs (Wurzelhaare); the first is true, but the latter 
assertion is not quite correct. As shown in figs. 100 and 101, short filaments are 
here and there given off from the under side of the basal layer; these filaments 
have first the character of unicellular rhizoids, but increase in length and form 
long septate filaments running under the primary basal layer, and in older crusts 
they may form a continuous layer consisting of one to more layers of variously 
disposed cells, the undermost of which may have the character of rhizoids pene- 
trating into the unevennesses of the substratum, while the upper cells in thicker 
fronds resemble those of the primary basal layer. According to Scumirz and Haupr- 
FLEISCH (I. c.), rhizoids are frequently produced in the undermost part of the cor- 
tical layer. 
