ST AURA STRUM. 153 



SCOTLAND.- -Plankton of Loch Fadaghoda, Lewis, 

 Outer Hebrides ! 



G ('(></,. Distribution.- -Siberia. 



Forma TRIGONA nob. St. sibericum Borge forma trigona 

 W. & G. S. West, New and Int. Freshw. Alg. 1896, p. 

 157, t, 4, f. 39; Alg. S. England, 1897, p. 493; Some 

 Desm. U. S. 1898, p. 312. Vertical view triangular with 

 slightly concave sides and subacute angles. Length 



*/ O 



13'5-16'5ju; breadth 15-16 ju ; breadth of isthmus 3*8- 

 8'6 fi. 



ENGLAND. - - Devil's Jumps, Frensbam Common, 

 Surrey ! 



Geugr. Distribution.- -United States. 



One specimen of this form was noticed with a wide 

 gelatinous investment 39 n in diameter. 



18. Staurastrum inelegans AY. & Gr. S. West. 

 (PI. CXXIV, figs. 2-4.) 



Staurastrum inelegans W. & <3r. S. West, Further Coiitrib. Freshw. Plank- 

 ton Scott. Lochs, 1905, p. 501, t. 7, f. 11, 12 ; Brit. Freshw. Phytoplank- 

 ton, etc., 1909, p. 182. 



Cells of medium size, as long as broad or a little 

 broader, deeply constricted, sinus very wide and 

 obtusely rounded at the extremity, isthmus shortly 

 cylindrical ; semicells widely subtriangular, inferior 

 margins almost straight or slightly biundulate, dorsal 

 margin (apex) convex in the middle, angles produced, 

 acute or apiculate (rarely subobtuse). Vertical view 

 triangular, sides convex in the middle, angles sub- 

 mamillate and slightly apiculate. Cell-wall smooth. 



Zygospore unknown. 



Length 53'5-60 p. ; breadth 51-62 p. ; breadth of 

 isthmus 9-10 p. 



SCOTLAND. Plankton of Loch Fadaghoda, Lewis, 

 Outer Hebrides ! 



This remarkable Staurastrum, so far only observed from 

 the one locality, is somewhat variable in its characters. The 

 angles of the semicells are generally produced, and either 

 acute or apiculate, but in some specimens they are relatively 



