544 MR. W. WEST AND PROF. G. 8. WEST ON 
Var. EXCAVATUM, var.n. (PI. 17. fig. 5.) 
Var. cum sinu latissime excavato et isthmo elongato-cylindrico. 
Long. sine spin. 26-27; lat. sine spin. 16-19»; long. spin. 
21-29 p; lat. isthm. 8°5 p. 
Hab. Loch Shin, Sutherland. 
Var. SUBEXCAVATUM, var.n. (PI. 17. figs. 6-8.) 
Var. corpore minore et spinis validioribus; sinu excavato et 
isthmo subcylindrico. 
Long. sine spin. 25-28 » ; lat. sine spin. 16-18 » ; long. spin. 
25-31 p; lat. isthm. 6°5-7 p. 
Hab. Loch Ruar, Sutherland (J. Murray)! 
17. STAURASTRUM ARISTIFERUM, Ralfs, Brit. Desm. 1848, 
p- 128, t. 21. f. 2. 
Var. PROTUBERANS, var. n. (PI. 14. fig. 5.) 
Var. apicibus cellularum in medio valde convexis ; semicellule 
a vertice vise triangulares, lateribus in medio convexis. 
Long. sine spin. 23-27 p; lat. sine spin. 24-27 »; long. spin. 
13°5-17 p; lat. isthm. 9°7 p. 
Hab. Loch Nan Eun, N. Uist, Outer Hebrides. 
This variety differs principally in the convex apices of the 
semicells, and in the convex swelling in the middle of each side 
of the vertical view. 
18. S. MEGAcANTHUM, Lund. in Nov. Act. R. Soc. Scient. 
Upsala, ser. 3, viii. (1871) no. 2, p. 61, t. 4. f. 1. 
Var. sCoTIcUM, var. n. (PI. 16. fig. 8.) 
Var. apicibus cellularum rectis vel leviter concavis, sinu paullo 
apertiore, spins longioribus et leviter divergentibus. 
Long. sine spin. 35-44 y; lat. sine spin. 38-51 p, cum spin. 79- 
lll yp; long. spin. 19-34; lat. isthm. 10°5 p. 
Hab. Loch Shin, Sutherland. Loch Doon, Ayrshire. 
This variety varies considerably in size, and is unquestionably 
the plant described and figured by Borge as “? S. megacanthum, 
Lund. forma” from plankton collected in the Isle of Mull. It 
is readily distinguished from typical S. megacanthum by the 
slightly hollow apices, of the cells and the longer, slightly diver- 
gent spines. 
