516 MR W. WEST AND MR G. 8. WEST ON 
DESCRIPTION OF PLATES. 
Puate 1. 
Photomicrographs of plankton from Loch Ruar, Sutherland ; all x 100. 
No. 1. 1, Mougeotia sp.; 2, Cosmarium contractum ; 3, Staurastrum gracile; 4, St. paradoxum ; 5, St. 
jaculiferum, f£. biradiata; 6, St. cuspidatum, var. maximum; 17, Asterionella gracillima; 8, Tabellaria 
fenestrata, var. asterionelloides ; 9, Surirella robusta, var. splendida; 10, Celospherium Kiitzingianum. 
No. 2. 1, Huastrum verrucosum, var. planctonicum ; 2, Staurastrum jaculiferum ; 3, St. cuspidatum, var. 
maximum; 4, St. paradoxum, var. longipes; 5, St. Arachne, var. curvatum ; 6, St. erasum ; 7, Tabellaria 
fenestrata and var. asterionelloides; 8, Fragilaria Crotonensis, var. contorta; 9, Surirella robusta, var. 
splendida. 10, Ceratiwum hirundinella. 
No. 3. 1, Euastrum verrucosum, var. reductum; 2, Cosmarium Botrytis, var. depressum; 3, St. jaculi- 
Serum, var. subexcavatum ; 4, St. dejectum, var. inflatum ; 5, St. paradoxum ; 6, St. erasum; 7, Tabellaria 
Senestrata, var. asterionelloides ; 8, Asterionella gracillima; 9, Surirella robusta, var. splendida ; 10, Anurea 
cochlearis. 
No. 4. 1, Pleuroteniuwm Ehrenbergii; 2, Huastrum verrucosum, var. reductum; 3, St. jaculiferum, f. 
biradiata ; 4, St. dejectum, var. inflatum ; 5, St. gracile ; 6, St. paradoxum; 7, St. erasum; 8, Sphxrocystis 
Schroeterii ; 9, Tabellaria fenestrata, var. asterionelloides; 10, Surtrella robusta, var. splendida ; 11, Cocconema 
gastrotdes. ae 
No. 5. 1, Mougeotia, sp.; 2, Closterium rostratum; 3, Huastrum verrucosum, var. reductum; 4, E. 
verrucosum, var. planctonicum ; 5, Cosmarium Botrytis, var. depressum; 6, Stawrastrum paradoxum ; 7, St. 
jaculiferum; 8, Asterionella gracillima; 9, Fragilaria Crotensis, var. contorta; 10, Tabellaria fenestrata, 
var. asterionelloides ; 11, Surtrella robusta, var. splendida ; 12. Ceratiwm hirundinella; 13, Anurxa cochlearis. 
No. 6. 1, Micrasterias Murrayt; 2, Staurastrum jaculiferum, forma biradiata; 3, St. paradoxum ; 4, 
St. paradoxum, var. longipes ; 5, St. erasum ; 6, Pediastrum duplex ; 7, Tetraédron limneticum ; 8, Asterion- 
ella gracillima; 9, Tabellaria fenestrata, var. asterionelloides; 10, Surirella robusta, var. splendida; 11, 
Anurea cochleuris. 
Prarn 2. 
Photomicrographs of plankton from Loch Ruar, Sutherland. Nos. 1 and 2 x 500; Nos. 3-6 x 200. 
No. 1. Tabellaria fenestrata, var. asterionelloides This shows the most frequent form of this variety. 
No. 2. Tabellaria fenestrata, var. asterionelloides. A more slender form, with fewer cells in the colony. 
This form is much more rarely met with than No. 1. 
No. 3. 1, Stawrastrum jaculiferum, forma biradiata; 2, Asterionella gracillima; 3, Tabellaria 
fenestrata, var. asterionelluides. 
No. 4. 1, Ewastrum verrucosum, var. planctonicum ; 2, St. jaculiferum, forma biradiata; 3, Tabellaria 
Jenestrata, var. asterionelloides; 4, Asterionella gracillima i 5, Surirella robusta, var. splendida; 6, 
Dinobryon, sp. 
No. 5. 1, Staurastrum jaculiferum, forma biradiata; 2, Spherocystis Schroeterii; 3, Pediustrum 
Boryanum ; 4, Fragilaria Crotonensis, var. contortu. 5, Anurea cochlearis. 
No. 6. 1, Huastrum verrucosum, var. reductum; 2, Staurastrum erasum ; 3, Spherocystis Schroeterit ; 
4, Surirella robusta, var. splendida. 
PuatE 3. 
Photomicrographs of plankton from Loch Fadaghoda, Lewis, Outer Hebrides ; all x 100. 
No. 1. 1, Staurastrum Ophiura ; 2, St. longispinum (the wide gelatinous investment of this species is 
just visible in the original photograph) ; 3, S¢. Sebaldi, var. productum; 4, St. jaculiferum (forms) ; 5, St. 
gracile ; 6, Xanthidium antilopeum; 7, Mougeotia, sp. ; 8, Tabellaria fenestrata. 
No, 2. 1, Staurastrum Ophiura; 2, St. grande; 3, St. anatinum, var. grande ; 4, St. anatinum, var. 
truncatum ; 5, St. jaculiferum ; 6, St. dejectum; 7, Spirogyra, sp.; 8, Spherocystis Schroeterii ; 9, Tabellaria 
fenestrata ; 10, Astertonella gracillima; 11, Ceratiwm hirundinella; 12, Anurea cochlearis ; 13, Polyarthra 
platyptera. 
