18 
NEW OR CRITICAL BRITISH ALGiE. 
Halothrix lumbricalis , Rke., Desmotrichum undulatum , Rke., Pune - 
taria latifolia , Grey., Ect. fasciculatus, Harv., etc., which conceal 
its tiny fronds from view, its discovery is rendered still more diffi- 
cult. My specimens are only from 1*5-2 m.m. in length, although 
Baltic specimens are said to reach 10 m.m. The fronds are simple, 
for the most part composed of a single row of cells, with here and 
there a longitudinal septum, and an occasional hyaline hair. More 
rarely the frond is composed throughout of from 2-3 rows of cells. 
The plurilocular sporangia appear either as conical protuberances 
with broad bases, sessile on the vegetative cells, or are formed in 
the continuity of the frond by transformation of the cells, frequently 
5 or 6 contiguous cells being transformed into sporangia. 
Unilocular sporangia unknown. 
Pesmotiichum undulatum, Ulce. Algenfi. p. 55. Attus t. 11. 
Weymouth. 
In our revised list of British Marine Alga3,* Mr. Holmes and 
I have admitted this species on the authority of a specimen in the 
Greville Herbarium labelled Punctaria tenuissima, Grev., in 
Greville’s own writing. The specimen is a mixture of Punctaria 
latifolia, var. Zosterce, Lyngb. (in fruit), and Scytosiphon lomen- 
tarius , Ag., with a few fronds of what appears to be the present 
species, but owing to the age of the specimen it is difficult to 
examine it accurately, and consequently to form a Correct opinion 
as to the species. I am glad, therefore, to be able to report the 
discovery of undoubted specimens of D. undulatum, Rke. My 
specimens are very small, being only 5 to 6 m.m. long, while Baltic 
specimens sometimes attain to 12 centimetres in length, but are 
well fruited, leaving no possible doubt as to the genus and species 
to which they belong. D. undulatum may always be known from 
D. balticum by the fact that there are many cells, usually from 
6-40, but always more than 2, in the width of a frond. A section 
also shows the frond to be composed of from 2-4 layers. The 
frond is also much more thickly covered with scattered hyaline 
hairs than is the case with D. Balticum. 
Pogotrichum filiforme. Bice. Atlas , t. 41, figs. 12-25. — Forma gracilis, 
nov. form. 
In his “ Atlas Deutscher, Meeresalgen” Dr. Reinke figures and 
describes a plant found by Major Reinbold in Heligoland in June, 
1888, which although in many respects like a Litosiphon he has 
made the type of a new genus, Pogotrichum. Both in the Gare 
Loch and at Weymouth I have found an alga agreeing in all 
essential particulars with the Heligoland plant, for specimens of 
which I have to thank Major Reinbold, but more slender, the 
fronds usually consisting of only one row of cells, filaments with 
more than a single row being very rarely met with. I propose to 
* This list can now be procured in a separate form from the publishers 
of the “ Annals of Botany.” 
