122 BRITISH CHAROPHYTA. 



Habitat. — In pits, pools, and water-courses in peaty- 

 districts, and in one lake ; rare. 



Distribution.— i?/?^Zrt7;(/ .• Norfolk, W., turf-pool,. 

 Lopham Great Fen {G. B. B.-W., 1897); Cambridge- 

 shire, peat-pits, Bottisham, Burwell, and Wicken Fens, 

 and in Wicken Lode; fen near Clayhitlie {W. A.. 

 Leighton, 1831). 



Wales : Anglesey, Cors Bodeilio and Cors Ddraenog 

 (J. E. Griffith, 1882) ; peat-pools, Llanfl&nnan, East of 

 Llangefni (0. Bailey, 1884). 



Ireland : Westmeatli, peat-pits, Scraw Bog, near- 

 Loughanstown {H. G. Levinge and H. ^' J. G., 1892) ; 

 Lough Owel {G. R B.-W., 1904); Gahvay, N.E. 

 Ballindooly (H. ^ J. G., 1892). 



First record (as C. gracilis) : Henslow Catalogue,. 



1829. 



Outside the British Isles N. tenuissima is recorded 

 from Sweden, Spain, France, Germany, Switzerland,. 

 Hungary, Italy, Dalmatia, and Greece ; also from N. 

 Africa, Asia, N. America, and the West Indies. 



Usually quite a small plant, often not more than 10 cm. 

 in height. Specimens from Wicken Fen have however been 

 collected by G. R. B.-W., 20 cm. high, and from Galway 

 by H. & J. Gr. a rather drawn-out form still taller. The 

 Anglesey plant is very small, som'e of the whorls being not 

 more than 2'5 mm. across. 



The very slender stem, short branchlets, and distant, 

 whorls give this species a very distinct appearance, and it 

 cannot well be mistaken for any of the other British Nitellse,. 

 with the exception of N. batrachosperma. From that species, 

 it differs by the absence of oogonia and antheridia at the 

 first furcation of the branchlets and by the remarkable 

 decoration of the membrane. The uniformly 2-celled ultimate- 

 rays of the fruiting whorls distinguish it from any form 

 of N. gracilis. Sometimes in the sterile branchlets of' 

 JV. tenuissima, owing to there being only one ray produced 

 at the last node, it may appear to have a 3-celled ultimate ray. 



The lai-ge number of rays at each furcation cause the 

 whorls often to be almost globular, and extreme forms arc 

 remarkably moniliform (PI. XIV, f. 2). The stems are but. 

 little branched. It is often densely incrusted with lime. 



