548 MR. W. WEST AND PROF. G. S, WEST ON 
This species bears considerable resemblance to S. pelagicum, 
West & G. S. West (in Trans. Roy. Irish Acad. vol. xxxn. 
part 1 (1902) p. 46, t. 2. ff. 26, 27), but is distinguished by the 
different form of the semicells and the more open sinus and by 
the processes. The processes of S. pseudopelagicum are hollow, 
containing part of the cell-cavity, whereas those of S. pelagicum 
are solid projections of the celi-wall. 
S. pseudopelagicum might also be compared with some forms 
of 8. paradoxum, Meyen, but is readily distinguished by its 
shorter processes, which are terminated by two large divergent 
spines situated in the same vertical plane. 
29. SraurastRUM PARADOXUM, -Veyen, 1829; Ralfs, Brit. 
Desm. 1848, p. 138, t. 23. f. 8. 
Many of the plankton forms of this species are considerably 
rougher than ordinary examples. The processes are adorned 
with short papille instead of granules, and near their bases 
these papilla become short spines. 
The two following forms are deserving of special mention :— 
Forma a.—A_ triangular form with the processes short and 
only slightly diverging. 
Long. sine proc. 33 », cum proe. 51 p ; lat. cum proce. 65-68 p ; 
lat. isthm. 12°5 p. (Pl. 18. fig. 5.) 
Hab. Loch Tay, Perthshire. 
Except for the three diverging spines at the apices of the 
processes, this form greatly resembles St. pseudopelagicum. It 
also closely resembles S. Magdalene, Birgesen (‘ Phytoplankton 
of Lakes in the Ferées,” Bot. of Ferées, 1903, pp. 618-619, 
fig.148); in fact the latter has the appearance of some of the 
plankton-forms of S. paradoxum with spines instead of granules 
or papille and quadrifureate apices to the processes. 
Forma 6.—A quadrangular form with the processes of normal 
length and more diverging ; also with a row of papillations along 
the upper margins of the semicells (visible within each lateral 
margin in the vertical view). 
Long. sine proc. 37 », cum proc. 63; lat. cum proc. 63 4; 
lat. isthm. 14 4. (Pl. 18. fig. 4.) 
Hab. Loch Laxadale, Harris, Outer Hebrides. 
Var. CINGULUM, var. n. (PI. 18. figs. 6, 7.) 
Var. processibus longioribus et tenuioridbus, sursum gracile 
curvatis ; apicibus semicellularum rectis vel convexis ; basi 
