_ 
7 
"er 
SCOTTISH FRESHWATER PLANKTON. 549 
semicellularum angustiore et subcylindrica, cum annulo spinarum 
minutarum circ. 12 (visis 7). 
Long. sine proc. 32-40 p, cum proc. 71-81 py; lat. sine proc. 
circ. 16-23 p, cum proc. 64-77 »; lat. bas. semicell. 11°5-12 p ; 
lat. isthm. 7°5-8°5 p. 
Hab. Loch Shin, Sutherland. Lochs Katrine and Achray, 
Perthshire. 
This variety is distinguished by the narrow, cylindrical base of 
the semicells furnished with a ring of about a dozen minute 
spines. The processes are longer than in typical forms and are 
gracefully curved upwards. The body of the semicell is fre- 
quently covered with small granules, similar to those on the 
processes and arranged in concentric rings round the base of 
each process. In length and in curvature the processes are 
similar to those of S. paradoxum, var. longipes, Nordst. 
30. SrauRasTRUM GRACILE, Ralfs, in Ann. § Mag. Nat. Hist. 
Xv. (1845) p. 155, t. 11. f. 3; Brit. Desm. 1848, p. 136, t. 22. 
f. 12. 
A form with the processes horizontally disposed, but curved 
upwards towards their apices ; with a few large granules at each 
side of the base of every process. 
Long. sine proc. 52; lat. cum proc. 96-102 p; lat. isthm. 22 p. 
Hab. Loch Shin, Sutherland. 
31. S. Anacune, Ralfs, in Ann. & Mag. Nat. Hist. xv. (1845) 
p. 157, t. 11. f. 6; Brit. Desm. 1848, p. 136, t. 23. f. 6. 
Var. curvaruMm, var. n. (PI. 18. fig. 9.) 
Var. processibus leviter extrorsum curvatis ; a vertice vise 4- 
vel 5-radiatm, 
Long. 30; lat. sine proc. 18 », cum proc. 57-70 p; lat. 
isthm. 9 p. 
Hab. Loch Nan Cuinne, Sutherland (J. Murray) ! 
This variety is either 4- or 5-radiate, and differs from all other 
forms of §. Arachne in the outwardly curved processes, a 
character which was constant in all the specimens examined. 
32. S. verriciunatuM, Archer, in Quart. Journ. Mier. Sci. new 
Ser. ix. (1869) p. 196. 
. Long. sine proc. 76-79 «4; cum proc. 136-143 p; lat. sine proc. 
cire, 36-38 «x, cum proc. 124-130 p; lat. isthm. 20 p. 
Hab. Loch Mor Bharabhais, Lewis, Outer Hebrides. 
