430 MR. W. WEST AND PROF, С. S, WEST ON THE 
the British Islands is very largely (but not entirely) dependent upon the 
presence of the requisite physiological conditions for the growth of these 
plants, such conditions being in all probability determined by the degree of 
concentration of the dissolved salts in the water. 
It seems likely that with our present knowledge of the occurrence and 
distribution of. British Desmids the whole matier could be definitely settled 
by a careful and exact chemical investigation of the waters of the lake-areas, 
both of the lakes and the bogs. 
DESCRIPTION OF SOME NEW FORMS FOUND IN THE PHYTOPLANKTON. 
The following new forms have been observed during the foregoing 
investigation :— 
1. Roya camprica, W. & G. S. West, in Journ. Bot. 1903, p. 41, t. 446. 
Ё. 11; Monogr. Brit. Desm. i. 1904, р. 108, t. 10. f. 81. 
Forma riMxETICA, W. & G. S. West. (01. 19. figs. 11, 12.) 
Forma apicibus eellularum valde truncatis, pyrenoidii in cellula. tota 10, 
Long. cell. 141-183 р; lat. med. cell. 6 ш; lat. apie. 44-5 p. 
Hab. Loch Katrine (June 1909). 
2. SPONDYLOSIUM PLANUM, (Wolle) W. & G. S. West. Sphærozosma 
pulchrum, Bail, var. planum, Wolle, Desm. U. S. 1884. р. 29, t. 4. ff. 3, 4. 
Spondylosium pulchrum, (Bail.) Arch., var. planum, W. & G. S. West, in 
Journ. Linn. Soc., Dot. xxxiii. 1898. p. 211; ibid. xxxv. 1903, p. 551; ete. 
Spondylosium pulchrum, Bachmann, in Archiv für Hydrobiol. u. Plankton- 
kunde, iii. 1907, p. 30. 
S. mediocre, filis non tortis, sine vagina mucosa : cellule circiter 11-plo 
latiores quam longie, subquadrate, angulis rotundatis, profunde constrict, 
sinu aperto et obtuso; semicellule transverse oblongz, angulis rotundatis, 
apice recto; semicellulw а vertice vise oblong polis rotundatis, a latere 
vise subcireulares; membrana glabra. 
Long. cell. 115-195 д; lat. 12-25 ws lat. isthm. 5-115 и: crass. 
6-11 ш. (РІ. 19. figs. 5-8.) 
Hab. Fairly general in the plankton of all the British lake-areas. 
We have placed this Desmid as a species because there ix no possibility of 
confusing it with any other Spondylosium. It varies much in size, but 
retains its characters with great constancy. It has little, if any, relationship 
to S. pulchrum, (Bail.) Arch., differing in its much smaller size, in its plane 
and untwisted filaments, and in the flattened closely applied apices of the 
semicells. The semicells are of a different form from those of S, pulehrum. 
