THE FRESHWATER PLANKTON OF THE SCOTTISH LOCHS. 507 
ease, which is the number usually present in P. ilinowsensis, Kofoid, but the relatively 
large size of the gonidial cells, and the fact that the vegetative cells constitute 
about one-half of the colony, are characters more in agreement with P. californica, 
Shaw. The gonidial cells contained a large chloroplast, in which was imbedded a single 
pyrenoid, often of considerable size. 
Whether these colonies should or should not be regarded as belonging to a genus 
closely allied to Hudorina, but distinguished by a differentiation of reproductive from 
vegetative cells, or merely as ‘“‘ Pleodorina-stages” of Hudorina elegans, is a question 
for further investigation. 
Family Protococcacr& (or AUTOSPORACE). 
Genus Calastrum, Nig., 1849. 
41. C. Morus, W. & G. 8. West, in Journ. Bot., Sept. 1896, p. 5 (sep.), t. 361, f. 4. 
Diam. cell. 17-19»; diam. colon. 50-53 p», (Pl. 6, fig. 12). 
Hab.—Loch Fadaghoda, Lewis, Outer Hebrides. 
Genus Tetraédron, Kiitz., 1845. 
42. T. limneticum, Borge, ‘‘ Schwedisches Siissw. Plankton,” Botaniska Notiser, 
1900, p. 5, t. 1, f 2. 
Diam. cell. 53-62 » (Pl. 6, figs. 10, 11). 
Hab.—Loch Ruar, Sutherland (J. Murray)! 
The specimens were slightly smaller than Borcr’s Swedish ones, and the bifurcations 
of the extremities more marked. 
Genus Botryococcus, Kiitz., 1849. 
43. B. protuberuns, sp. n. (Pl. 4, No. 4, pl. 6, figs. 8, 9). 
Cellulze in coloniis irregularibus, familiarum associatarum compositis ; familie e 
4, 8, 16, plusve cellularum formate ; cellule anguste cuneatze vel ovate, cum mucila- 
gine adhzerentes, cellule periphericee subdistantes et exertee ex massa mucilaginis, solum 
ad partem angustiorem adherentes, parte latiori libera extrorsum directa. 
Diam. colon. circ. 100-220 u; long. cell, 16°5-20 u; lat. max. cell. 9°5-11°5 uw. 
Hab.—Loch Fadaghoda, Lewis, Outer Hebrides. 
This species is readily distinguished by the few cells which form the smaller 
aggregations, and by the prominent way in which they project from the mucus in 
which they are imbedded. The colonies reach a large size and frequently become dark 
in colour. Living specimens were not seen, and it was quite impossible to arrive at 
any definite conclusions as to the nature of the chloroplast from the specimens preserved 
in formalin. 
The cells are ovate or cuneate in shape, and are imbedded by their narrower ends 
im amass of mucus. Lach of these small aggregations or families consists of 4, 8, or 16 
