STAURASTROI. 129 



Cells rather under medium size, slightly longer than 

 broad, including the processes, constriction fairly deep ; 

 semicells elliptic-subsemicircular. ventral margin strongly 

 convex, dorsal margin slightly so, angles produced to 

 form short thick processes, slightly divergent, terminated 

 by 4 short spines, and with 2 or 3 circles of strong 

 denticulations. Vertical view triangular, sides slightly 

 convex, angles produced into short thick processes, 

 which are distinctlv denticulate. Cell-wall rough with 



/ o 



minute granules, arranged in concentric series round the 

 base of the processes. 



Zygospore unknown. 



Length, without processes, 37-40 [JL ; breadth, without 

 processes, about 29-33 u. ; breadth, with processes, 

 44-55 [i ; breadth of isthmus 10'5 JJL. 



SCOTLAND.- -Plankton of Xeugles Water and Loch 

 Brindister, Shetlands ! 



This species was found in abundance in the plankton of the 

 above-mentioned lakes. Its distinctive characters are the large 

 size of the " body" of the semicells., and the short, outwardly 

 diverging processes, each of which possesses 2 rings of denticu- 

 lations and 4 apical spines. It is perhaps nearest to St. poly- 

 morphum Breb., but is larger, of different relative proportions, 

 and with different processes. 



132. Staurastrum proboscidium (Breb.) Arch. 

 (PI. CXLIII, figs. 14-16.) 



Staurastrum aspcrum var. proboscidium Breb. in Ralfs, Brit. Desni. 1848, 



p. 139, t. 23, f. 12, b, c. 

 St. proboscidium Arch, in Pritch. Infus. 1861, p. 742 ; Jacobs. Desm. Danein. 



1875, p. 206 ; Cooke, Brit, Desm. 1887, p. 173, t. 59, f . 6 ; De Toni, 



Syll. Alg. 1889, p. 1215 ; Comere, Desm. de France, 1901, p. 151, t. 11, 



f. 10 ; West & G. S. West, Freshw. Alg. Orkneys and Shetlands, 1905, 



p. 28 ; Borge, Botan. Notiser, 1913, p. 31. 

 Didymidium (Staurastrum} polymorphum Reinsch. Algenfl. Frank. 1867, 



p. 165 (in part). 

 Staurastrum hexacerum v. ornatum Borge, Siissw. Chlor. Archang. 1894, 



p. 37, t. 3, f. 43 (form). 

 St. Borgeanum Schmidle, Lappm. Siisswasseralgen, 1898, p. 60, t. 3, f. 7 ; 



West & G. S. West, Notes Alg. II, 1900, p. 297, t. 412, f. 10 ; Alga-fl. 



Yorks. 1902, p. 106. 

 ? St. proboscidium var. subglabrum West, Alg. N. Wales, 1890, p. 19, f. 35. 



VOL. V. 9 



