294 DR. LILY BATTEN ON 
References. Agardh (2) ii. p. 1055 ; De Toni (22) iv. p. 942; Falken- 
berg (24) p. 120 et seg. ; Hauck (31) p. 246. 
lcones, Kützing, Tab. Phye. xiii. & xiv. l. c. 
DESCRIPTION.—/abit. Plants from 1-9 ems. high. Branching alternate 
or pseudo-dichotomous in the principal branches, irregularly alternate in the 
smaller branches and ramuli, the ramuli being short and spine-like, and 
closely set on the shorter branches.  Siphons. 20 or more pericentral 
round central one of diameter roughly equal to the radius of the filament. 
Colour. Brownish, becoming black in drymg. Anatomy. Articulations 
usually about as long as broad, sometimes attaining a length of 14 times 
their breadth. During summer, tips of branches and ramuli clothed with 
colourless multi-ceilular diehotomising filaments. Attachment organ. 
Young plant attached at the base by rhizoids developed longitudinally from 
the pericentral siphons. Procumbent branches produce new rhizoids later, 
each having a disc at its extremity. Reproductive organs. Tetraspores 
intercalary in development, not always occupying successive articulations of 
the ramulus. Antheridia occurring in tufts on the terminal dichotomising 
fibrillæ, replacing some of the branches. Cystocarps ovate in form, sessile 
on the ramuli. 
Habitat. Occurring between the tide-marks. Rare. 
British Records, Petit Port, Guernsey. 
Distribution in Europe. Adriatic Sea. 
6. P. RicHaRDsont Hook. in Smith's English Flora, v. 1833, p. 333. 
Reference. De Toni (22) iv. p. 920. 
Icones. Harvey, Phye. Brit. pl. 10. syn. 111. 
Descriprion.— Habit. Plants attaining a length of 8-10 cms. Main axis 
much branched and zigzag in form, with lateral branches arising at an angle 
of nearly 90°. Ramuli slender and like the branches, alternate in origin. 
Siphons. 5 round a smaller central. Colour. Reddish-brown, becoming 
darker in drying. Anatomy. Articulations three or four times as long as 
broad in the middle parts of the plant, where the pericentral siphons 
are spirally twisted. Articulations shorter and siphons parallel to the long 
axis in the upper parts. Attachment organ. Examination of Richardson’s 
specimen in the Herbarium Hookerianum at Kew shows a disc-like attach- 
ment organ comparable to that of P. elongella. Reproductive organs. Cysto- 
carps borne near the tips of the branches, globose and sessile with a wide 
ostiole. 
De Toni (22. iv. p. 920) suggests the possibility of P. Richardsoni Hook. 
being synonymous with P. rhunensis Thur., but this is not practical, owing 
to the anatomy of the plant, the total difference of attachment organ, and the 
difference of habit. 7°. Richardsoni Hook. is probably near to P. collubens 
