OLOSTERIUM. 155 



Cells moderately large, aboul 12-14 times longer 

 than their diameter, slightly curved, outer margin 

 30-32 of arc, inner margin almost straight except 

 towards the poles where it is slightly concave, gradu- 

 ally attenuated towards the apices, which are acute 

 (or rarely acutely rounded) ; cell-wall smooth and 

 colourless; chloroplasts with about six ridges and a 

 central series of about four to six pyrenoids ; terminal 

 vacuoles with several small moving granules. 



Zygospore unknown. 



Length ISO -30:', p. ; breadth 12-17'5/x. 



ENGLAND. Hawclii'fe Common, W. Yorks ! Near 

 Senens, Cornwall ! 



IRELAND. Gortahork, Donegal ! 



< <<'<></ r. ])ixlrilnitn>n. France. W. Africa. 



This species should not, perhaps, be separated from (7. 

 Nti-iyoxiitii Brcb. It is distinguished from Brebisson's species 

 by its somewhat smaller size, its relative shortness, and its 

 apices, which are not incurved. 



Var. elegans G. S. West. (PL XIX, figs. 12, 1:5.) 



Cl. peracerosum var. elegoMs G. S. West, Alga-fl. Cambr. 1899, p. Ill, 

 t. 396, f. 1, 2. 



Cells more graceful, more attenuated and curved 

 towards the apices, ventral margin slightly tumid in 

 the middle, apices narrow but obtuse; chloroplasts 

 with a series of 5-8 pyrenoids ; apical vacuoles sub- 

 terminal, with one or two moving granules. 



Length 190-258 /A; breadth 14-1 5 p. 



ENGLAND. Comberton and Sutton West Fen, Cam- 

 bridge ! 



32. Closterium littorale Gay. 

 (PL XIX, fig. 14.) 



Closterium littorale Gay, Monogr. loc. Conj. 1884, p. 75, t. 2, f. 17 ; 



De Toni, Syll. Alg. 1889, p. 848 ; West & G.' S. West, Alg. S. England, 



1897, p. 481 ; Alga-fl. Yorks. 1900, p. 53. 

 Arthrodia litto rails Kuntze, Eevis. gen. plant. 1891, p. 883. 



