STAURASTRUM. 143 



Lancashire ! Ilkley, W. Yorks ( W. H. Dikes) . Surrey ! 

 Sussex (Rolfs). Hants ! Devon ! Cornwall ! 



WALES.- -Capel Curig ! (Gooke and Wills), Llyn 

 Padarn, and near Dolbadarn Castle, Carnarvonshire ! 

 Dolgelly, Merioneth ! (Ralfs). Plankton of several 

 of the Welsh lakes ! 



SCOTLAND.- -Sutherland ! Ross! Aberdeen, Kincar- 

 dine, Forfar, Perth ! (Roij $ Bissett). Plankton of 

 Loch Luichart, Ross ! Lewis, Outer Hebrides ! 



IRELAND.- -Near Westport, Mayo ! Gallery Bog, 

 Galway (Archer). Carantuohill, Kerry ! Dublin and 

 Wicklow (Archer). 



Geogr. Distribution.- -France. Germany. Galicia in 

 Austria. Norway. Denmark. Sweden. Bornholm. 

 United States. 



St. tumidum is one of the largest and most distinctive 

 British species of the genus. The cells are usually enveloped 

 in a large mucilaginous envelope, which may attain a 

 diameter of 196^. 



The semicells vary a little in outward form in front view 

 (Consult PL CXXII, figs. 1 and 3 a). The form with the 

 triangular vertical view is much the commonest, but tetra- 

 gonal forms are sometimes met with, and we have on one 

 occasion observed an irregularly pentagonal form. The 

 mamillate thickening at each angle is sometimes prominent, 

 but in other individuals it may be rather obscure. 



12. Staurastrum conspicuum W. & G. S. West. 



(PL CXXI, figs. 1, 2.) 



Staurastrum conspicuum W. & G. S. West, Scott. Freshw. Plankton, I. 

 1903, p. 547, t, 14, f . 4 ; Further Contrib. Freshw. Plankton Scott. Lochs, 

 1905, p. 486 ; British Freshw. Phytoplankton, etc. 1909, p. 181. 



Cells very large, about 1-^ times broader than long, 

 very deeply constricted, sinus linear in the median 

 part, widely open outwards, and dilated at its 

 extremity ; semicells elliptic-fusiform, dorsal margin 

 convex but widely truncate in the middle, lateral 

 angles strongly thickened and mamillate. Vertical 

 view triangular, sides widely concave, angles acutely 



