STAURASTBUM. 163 



Zygospore unknown. 



Length 42-53 ju; breadth 39*5-52 /x; breadth of 

 isthmus 16-22'5/x. 



ENGLAND. --Borrowdale, Cumberland ! Thursley Com- 

 mon, Surrey ! 



SCOTLAND.- -Plankton of Loch Luichart, Ross ! 

 Plankton of Loch Fadaghoda, Lewis, Outer Hebrides ! 



IRELAND.- -Lough Aunierin, and plankton of small 

 lakes between Clifden and Rpundstone, Gal way ! 



St. subpytjmasum is a well-marked species with an unfortunate 

 name, as it bears no relationship to "St. pygmaeum." We 

 have never seen it in great abundance, although it has been 

 frequent in some of the plankton-collections. It is a stout 

 Staurostrum, its general convexity and mamillate angles 

 giving it at once a distinctive character. The cell-wall is 

 usually distinctly punctate, hut in some individuals the 

 punctulations are so faint as almost to escape detection, and 

 in a few cases the cell-wall has appeared to be quite smooth. 

 To the latter forms we gave the name of " forma ylabra," 



Some specimens of this species develop a wide gelatinous 

 integument which may reach a diameter of 75 /u. 



Var. subangulatum car. nor. (PI, CXXIV, fig. 1.) 



Cells somewhat smaller than in the type, and more 

 deeply constricted ; semicells subrhomboid-elliptic, 

 angles less produced and thicker. 



Length 41 /x; breadth 41 /x; breadth of isthmus 9*5 /x. 



SCOTLAND.- -Loch Luichart, Ross ! 



26. Staurastrum corniculatum Lund. 

 (PI. CXXV, figs. 17, 18.) 



Staurastrum corniculatum Lund. Desm. Siiec. 1871, p. 57, t. 3, f. 23 ; 

 De Toni, Syll. Alg. 1889, p. 1150 ; Eoy & Biss. Scott. Desm. 1893, p. 180 ; 

 W. & Gr. S. West, Alg. S. England, 1897, p. 493 ; G. S. West, Alg. Yan 

 Yean, 1909, pp. 15, 27. 



Cells rather under medium size, H-l-r- times longer 



T 4: O 



than broad, slightly constricted, sinus a small obtuse 

 notch ; semicells widely subcuneate, gradually widened 

 from a broad base, sides very slightly convex f almost 



/ Or/ 



straight), apex straight, superior angles obliquely and 



