New British Freshwater Alyas. By W. and G. S. West. 157 
convexis, lateribus subparallelis, apicibus leviter convexis, vel 
trapezicae et subpyramidatae, angulis basalibns late rotundatis, 
lateribus subrectis subconcavisve, apicibus rectis, angulis 
superioribus cum spinis minutis 1-2, angulis inferioribus cum 
spinis minutis 1-4 ad marginem, intra margines et centrum 
versus spinis minutis paucis irregulariter dispositis praeditae ; 
a vertice visae ellipticae, ad medium utrobique tumore perparvo, 
polis rotundatis spinis minutis (in ambitu 3-6) obsessis. 
Long, sine spin. 18-27 /, i; lat. sine spin. 16-24 //,, cum 
spin. 19-25//,; long. spin. 0 * 8—1 • 2 yu. ; lat. isthm. 
5 * 5-9 *7 //, ; crass. 1 1 * 5-13 /x. 
Hab. Amongst Sphagnum, Orkney Islands. 
This is closely allied to X. Smithii Arch. var. variabile Nordst., 
but differs in the minute spines scattered over the surface of the semi- 
cells, especially towards the margins ; there are usually two or three 
within the margin at the middle of the apex (which show plainly in 
vertical view), and the spines also vary at the inferior angles from one 
to four. The vertical view also has the central protuberance less 
pronounced and in some cases almost obsolete ; the sinus, moreover, is 
not parallel but open. The specimen, fig. 22 a, very much resembles 
X. simplicius Nordst. 
Genus Staurastrum Meyen ; Ealfs. 
25. S. cuspidatum Breb. (Ealfs, Brit. Desm., p. 122, tab. xxi. 
fig. i). 
Var. divebgens Nordst. (Desm. Brasil., tab. iv. fig. 49). 
PI. IV. fig. 52. 
Zygosporae globosae mamillatae, unaquaque mamilla 
cum spina singula brevi ornata. 
Diam. zygosp. sine mam. 23*5-25 fi, c. mam. et spin. 
37-41 fi. 
Hab. Keston Common, Kent. 
The zygospore is somewhat similar to that of the type. 
26. S. corniculatum Lund (Desm. Suec., p. 57, t. iii. f. 23). 
PI. IY. fig. 37. 
Zygospora globosa, spinis longis delicatulis obsessa, 
apicibus spinarum profunde divisis, divisionibus patentibus. 
Diam. sine spin. 31 fi, c. spin. 63 fi; long. spin. 
15-19 ,1. 
Hab. Thursley Common, Surrey. 
Only one zygospore of this rare species was seen. 
27. S. sibiricum Borge (Siberiens Chlorophyllophyce-Flora, 
p. 9, f. 4). 
f. TRIGONA. PI. IY. fig. 39. 
A vertice visum lateribus tribus con ca vis. 
