496 MR W. WEST AND MR G. S. WEST ON 
Ill. Systematic Account or THE Morr ImportTanr ALG OF THE 
PLANKTON. 
This part of the paper deals specifically with the most interesting of the Algee found ; 
in the plankton. Many of these belong to the family Desmidiacez, in which the Scot- 
tish plankton is remarkably rich. Three species, viz., Stawrastrum inelegans, St. sub- a 
nudibrachiatum, and Desmidium occidentale, and a number of varieties, are here | 
described (and figured) for the first time, most of them having been found in Loch % 
Fadaghoda, Lewis. The following are rare Desmids which have not previously been | 
recorded from the British Islands :—Gonatozygon aculeatum, Hast. ; Hyalotheca Indica, 2 
Turn.; Micrasterias Wallichi, Grun.; Staurastrum sublevispinum, W. & G. §. cy 
West; and St. Tohopekaligense, Wolle, var. trifurcatum, W. & G. 8. West. | 
A new brown alga—Phzococcus planctonicus—oceurred in several of the lakes . 
examined, and the occurrence of Calastrum Morus, W. & G. S. West, is very . 
interesting. An undescribed genus of the Protococcoideee—Actinobotrys—oceurred in 
quantity in some of the lakes, and a few specimens of Pleodorina californica, Shaw, | 
were observed from Loch Fadaghoda. Botryococcus protuberans is also a well-marked 
new species. s 
Of the Diatoms, Fhizosolena eriensis, H. L. Sm., var. morsa, and Fragilara | 
Crotonensis (A. M. Edw.), Kitton, var. contorta, are worthy of special mention. : 
Class PH AOPHYCEA. 
Order SYNGENETIC&. 
Family PHaocapsacE&. 
Genus Pheococcus, Borzi, 1892. 
1. P. planctonicus, sp. n. (Pl. 6, figs. 15, 16). 
P. cellulis parvis, globosis vel subglobosis, 16-64 in tegumento libere natante agere- 
gatis; tegumentis gelatinosis, homogeneis, hyalinis et subellipsoideis, vix conspicuis; 
chromatophoris singulis vel binis, parietalibus, luteo-brunneis, cum marginibus irregu- 
lariter lobatis; membrana cellularum firma et tenue. Propagatio bipartitione cellularum 
in omnes directiones. 
Diam. cell. 7°2-9°6 w; diam. fam., 73-120 pm. 
Hab.—Loch Mor Bharabhais and Loch Fadaghoda, Lewis; and Loch Laxadale, 
Harris, Outer Hebrides. 
This alga is distinguished from the other species of the genus by its free-floating 
colonies of small size and its globose cells. Hach cell contains either one large, lobed 
chromatophore, occupying the greater part of the interior of the cell-wall, or two smaller, 
lobed chromatophores. 
The gelatinous investment is very inconspicuous, and towards its outer surface often 
exhibits a radiating fibrillar structure. 
