288 DR. LILY BATTEN ON 
curved in the main branches. Attachment organ. Young plant attached at 
the base by two rhizoids formed by longitudinal proliferation of basal siphons. 
Later, numerous rhizoids are formed by-lateral proliferation of procumbent 
branches, the siphons of which are parallel. Reproductive organs. Tetra- 
spores are intercalary in development, and are borne in the ramuli. 
Antheridia and cystocarps have not yet been recorded. 
The species somewhat resembles P. macrocarpa Harv. in outward appear- 
ance, but a slight torsion of the branches is visible to the naked eye, and 
the colour is much darker than in P. macrocarpa Harv. P. spiralis differs 
from P. platyspira Kütz. (87. xii. p. 63) in that the branching is not pseudo- 
diehotomous in the former species. The spiral twisting of the siphons is 
comparable to that of P. havanensis Kütz. (37. xiii. p. 72), but the branching 
and general habit of the plant are dissimilar. The large size of the central 
siphon makes it clear that the plant is not a young form of P. urceolata 
which is exhibiting a variation, and the length of the articulations bears out 
the view. P. macrocarpa, too, has a much smaller central siphon than 
P. spiralis. 
Habitat. On rocks and groins near low-water mark. 
British Records. Dorset at Durlston Head, Swanage, and between Sand- 
banks and the Haven. 
5. P. uRCEOLATA Grey. Flora Edinensis, 1824, p. 309. 
P. formosa Suhr (not Harvey) in Flora, xiv. (1831), p. 709. 
Grammita uncinata Bonnem. (not P. uncinata Kütz.) Ess. d'une class. 
des Hydro. loc., Journ. de Physique, xciv. 1822, p. 191. 
P. denticulata Kütz. Tab. Phyc. xiii. 1863, p. 28, tab. 90 (e-q). 
P. stricta Kütz. Tab. Phyc. xiii. 1863, p. 25, tab. 78 (d-q). 
P. patens Kitz. Tab. Phye. xii. 1863, p. 29, tab. 91 (c-e). 
Conferva urceolata Lightf. ex Dillw. p. 82, suppl. pl. G. 
References. Agardh (2) ii. p. 970; De Toni (22) iv. p. 875: Hauck (31) 
p. 221; Falkenberg (24) pp. 150, 152. 
Icones. Kützing, Tab. Phye. Le. Harvey, Phye. Brit. 1846-51, pl. 167. 
syn. 106. Æxsiceatw. Desmazieres, exsic. no. 1207, 1842. Lloyd, Alg. Ouest 
Fr. no. 174, 1854. Wyatt, Alg. Damnon. no. 133. 
Description.— /7abit. Occurring in tufts from 15-23 ems. long. Branching 
pseudo-dichotomous in the main branches, ramuli alternately branched and 
arising alternately, often flexed.  Siphons. 4 pericentral round minute 
central. Colour. Deep red. Anatomy. Length of articulations 3-5 times 
their breadth in the principal branches, approximately equal to their 
breadth in the lower parts of the plant and rather shorter in the ramuli. 
Attachment organ. Main axis of young plant attached at the base by one or 
two rhizoids, the central siphons of procumbent branches producing rhizoids 
