130 BRITISH DESMIDIAOEJE. 



Cl. Venn* it is distinguished by the straighter median portion 

 of tlie coll, by the thicker and more rounded apices, and by 

 its proportionately greater length. It also differs from both 

 these species in the nature of the terminal vacuoles, which 

 contain only one or two large moving granules. 



Var. robustum G. S. West. (PI. XV, figs. 20, 27.) 



Cl. Jenneri var. robustum G. S. West, Alga-fl. Cainbr. 1899, p. 112, t. 396, 

 f . 9 ; West & G. S. West, Alga-fl. Yorks. 1900, p. 50 ; West & G. S. 

 West, Alg. N. Ireland, 1902, p. 24 [erroneously reported as " var. 

 crassum"]. 



Stouter than the typical form, scarcely attenuated 

 towards the broadly obtuse apices. 



Distance between, apices (51-77 ju; breadth 12'5/x; 

 breadth of apices about 6-7*5 /x. 



ENGLAND. Pilmoor, N. Yorks ! Twenty-foot River, 

 between March and Guyhirne, Cambridge ! 



IRELAND. North of Newcastle, Down ! 



18. Closterium incurvum Breb. 

 (PI. XV, figs. 28-30.) 



Closterium innn-vum Breb. Liste Desm. 1856, p. 150, t. 2, f. 47 ; Arch, in 

 Priteh. Infus. 1861, p. 748; Rabenh. Flor. Europ. Algar. Ill, 186s, 

 p. 135; Delp. Desm. subalp. 1877, p. 102, t. 17, f. 22-27; DeTmii, Syll. 

 Alg. 1889, p. 843 ; Roy & Biss. Scott. Desm. 1894., p. 245 ; Nordst, Index 

 Desm. 1896, p. 144 ; West & G. S. West, Alga-ti. Yorks. 1900, p. 50 ; 

 Alg. N. Ireland, 1902, p. 24. 



Cl. Leibleinii Kiitz. b. minus Rabenh. Flor. Europ. Algar. Ill, ISlis, 

 p. 132. 



Cl. Dianx e. incurvum Klebs, Desm. Ostpreuss. 1879,, p. 12, t. 1, f. 14 if, b. 



Cells very small, 57 times longer than their diameter, 

 strongly curved, outer margin about 180 of arc, inner 

 margin not tumid, strongly attenuated towards the 

 apices, which are acute ; cell-wall smooth and colour- 

 less ; chloroplasts with several small pyrenoids in one 

 series ; terminal vacuoles with several small moving 

 granules. 



Zygospore globose and smooth. 



Distance between apices 52-64 /x ; breadth 10*5-14 a. 



ENGLAND. Pilmoor, N. Yorks ! Delamere, Cheshire 



