20 
NEW OR CRITICAL BRITISH ALG2E. 
By E. A. L. Batters, B.A., LL.B., F.L.S. 
Iiithothamnion roseum, Nov. Spec. 
Fronds saxicolous, thin, dark pink (never purple), lighter when 
dry, forming incrustations of indefinite extent, which are at first 
orbicular and covered with minute wart-like excrescences, after- 
wards indefinite in outline, the excrescences arising into short, 
erect, more or less cylindrical, prominent knobs from 5-8 mm. high 
and from 2-3 mm. in diameter, either simple, or bifid, or trifid 
above with blunt apices. Tetrasporic conceptacles hardly per- 
ceptibly raised above the surface of the frond, much compressed, 
with numerous orifices. Spores large, 140-200 p long, by 80-100 p 
broad, two-parted. 
Hab. Berwick. Cumbrae, St. Andrews (C. Howie and Hr. 
Axford.) 
This species is referred to on page 140 of my “ List of the 
Marine Algae of Berwick-on-Tweed ” as being probably distinct 
from L. polymorphum. At the time of writing that note (1889) 
I was uncertain whether my plant was identical with any described 
species, and consequently asked the opinion of Dr. Kjellman, who 
has devoted much time and attention to the study of this genus. 
He informed me that he regarded the plant as belonging to an un- 
described species. I have, however, from various causes, been pre- 
vented from describing the plant till the present. My first speci- 
mens were gathered at Berwick-on-Tweed, where the plant is far 
from uncommon. Mr. Holmes informs me he has received speci- 
mens from St. Andrews, gathered by Mr. C. Howie and Dr. 
Axford, and I have little doubt that the species on further investi- 
gation will be found at many stations around our coast. 
The plant grows on rocks and stones in deep pools, from half- 
tide level to below low-water mark of ordinary tides. It is usually 
accompanied by L. polymorphum , from which it may at all times be 
known by its colour, which is never purplish as in that species. 
At first the crusts are roundish and closely adherent to the sub- 
stratum, but when old they form wide, irregular patches several 
feet in diameter, portions of which can easily be detached from the 
rock. The species appears to be nearly related to L. colliculosum , 
Foslie, and since Foslie only found specimens bearing cystocarps 
it might be questioned whether my L. roseum were anything more 
than the tetrasporic form of that species. I, however, have speci- 
mens of a Lithothamnion , dredged from deep water near Cumbrae 
and in other portions of the Clyde sea area, which agree even 
better with Foslie’s description of L. colliculosum , in which the 
tetraspores are formed in prominent hemispherical or conical con- 
ceptacles with a single naked orifice, thus agreeing with the cysto- 
