BRITISH DESMIDTE^. 219 



A most remarkable and interesting plant, for a specimen of which I am 

 indebted to Professor Bailey. 



The triple terminal processes are so unlike what we find in other species of 

 Docidium, that Professor Bailey, in a letter to me, proposes to form a new 

 genus for the reception of this plant. 



Tab. XXXV. fig. 9. a. empty frond; b, c. empty segments ; d, e. extre- 

 mities highly magnified : from drawings by Professor Bailey. 



13. D. crenulatum (Ehr.). 



Closterium crenulatwn, Ehrenberg, Verbreitung und Einfluss des Mikrosk. 

 Lebens in Siid- und Nord-Amerika (1843). 



Professor Bailey informs me that this plant is identical with Docidium no- 

 dulosum. 



CLOSTERIUM, Niizsch. 



23. C. cuspidatum (Bailey) ; frond smooth^ crescent-shaped ; ends 

 mucronate. 



Closterium cuspidatum, Bailey, in lit. cum icone (1847). 

 Worden's Pond, Rhode Island, Bailey. 



Closteriutn cuspidatum differs from every other species of the genus in 

 having each end tipped by a spine or mucro. 



Tab. XXXV. fig. 1 1 . Frond : from a drawuig by Professor Bailey. 



24. C. Cucumis (Ehr.); frond smooth, stout, semilunate ; ends broadly 

 rounded. 



Closterium Cucumis, Ehrenberg, Verbreitung und Einfluss des Mikrosk. Lebens 

 in Slid- und Nord-Amerika, t. 4. f. 29 (1843). 



New York, Bailey. 



Ehrenberg' s figure represents this species about five times longer than 

 broad, in form resembling Closterium Lunula, but stouter in proportion to its 

 length, and having more rounded ends. 



25. C Thureti (Breb.) ; frond smooth, crescent-shaped; ends sub- 

 acute ; margins unconnected at the suture ; vesicles in a single 

 series. 



Closterium Thureti, Brebisson, in lit. cum icone (1846). 

 Falaise, Brebisson. 



26. C. arcuatum (Breb.) ; frond smooth, slender-crescent-shaped ; 

 ends obtuse, scarcely notched. 



Closterium arcuatum, Brebisson, in lit. cum icone (1845). 



