CLOSTERIUM. 137 



//) Enbridge Lake, Hants (Roy). Cornwall 

 ( Marquand). 



WALES. Capel Curig (Roy). 



SCOTLAND. Sutherland, Ross, Inverness, Nairn, 

 Aberdeen, Kincardine, Forfar, Perth, Stirling, Dum- 

 barton, Fife (Roy $ Uitisr-tt). Shetlands ! 



IRELAND. Lough Akibbon, Donegal! Carrantuohill, 

 Kerry ! 



Geuyr. Distribution. France. Galicia in Austria. 

 Italy. Sweden. Ceylon. Australia (var.). E. Africa. 



Some specimens of this species possess a very slight 

 depression or concavity on the outer margin close to the apex. 

 It is a rare Desmid. 



19. Closterium Venus Kiitz. 

 (PI. XV, figs. 15-20.) 



Closti.'1-iinn Venns Kiitz. Phyc. germ. 1845, p. 13O ; Kalfs, Brit. Desm. 1848, 



p. 220, t. 35, f. 11' ; Kiitz. Spec. Alg. 1849, p. 164 ; Kabenh. Flor. Europ. 



Algar. Ill, 1SI5S, p. 134 ; Wolle, Desm. U.S. 1884, p. 44, t. 7, f. G ; Hausg. 



Prodr. Algenfl. Bohm. 1888, p. 182 ; De Toni, Syll. Alg. 1889, p. 840 ; 



West, Alg. W. Ireland, 1892, p. 123 ; Eichler & Gutw. Nonn. spec. alg. 



nov. 1894, p. 163, t. 4, f. 3; Eoy & Biss. Scott. Desm. 1894, p. 21-9: 



Nordst. Index Desm. 1896, p. 267 ; West & G. S. West, Alg. S. England, 



1M97, p. 4,sl ; Alga-fl. Yorks. 1900, p. 50; Alg. N. Ireland, 1902, p. 23 ; 



Scott. Fresliw. Plankton I, 1903, p. 525. 



CL Diana? a. Venus Klebs, Desm. Ostpreuss. 1879, p. 12, t. 1, f. 14 c, c. 

 Arthfinlia Vcmis Kiintze, Revis. gen. plant. 1891, p. ssi. 

 Closterium trochiscosporum West & (Jr. S. West, New and Int. Fre.shw. 



Alg. 189(5, p. 151, t. 3, f. 16-20; W r est & G. S. W r est, Alg. S. England, 



1897, p. 481. 



Cells small, 8-9 times longer than their diameter, 

 strongly curved, outer margin 150 160 of arc, inner 

 margin not tumid, gradually attenuated to the apices, 

 which are acute or acutely rounded; cell-wall smooth, 

 colourless, or more rarely yellowish-brown ; chloro- 

 plasts ridged, with two pyrenoids (rnrely only one) ; 

 terminal vacuoles large, with a number of moving 

 granules. 



Zygospore oblong-rectangular with rounded angles, 

 shorter sides retuse, longer sides convex and inflated 

 in the middle ; often twisted, the two angles at one 

 end of the zygospore being disposed in a plane at 



