76 LIUTISH DESMIDIACE.E. 



W., X., and E. Yorks ! Lancashire ! Cheshire (/ 

 Leicester (Hoy). Warwick (Will*). Essex! Kent! 

 Surrey! Hants! Devon! Cornwall \ (Marquand). 



WALES. General in Carnarvonshire and Merioneth ! 



SCOTLAND. Common ! ; often with zygospores (Itoij A- 

 lUxwtt). Common in the Outer Hebrides ! Shetlands ! 



IRELAND. General in Galway, Kerry, and Donegal ! 

 Dublin and Wicklow (Archer}. Down! 



Geogr. Distribution. France. Germany. Austria. 

 Hungary. Xorway. Sweden. Italy. Russia. Lap- 

 land. Faeroes. Greenland. India. Ceylon. Singa- 

 pore. United States. Brazil. 



This is a widely distributed species, particularly in 

 mountainous districts. Its small size and its outward form, 

 which somewhat resembles certain species oiNavicula, render 

 it easy of identification. 



Liitkemuller considers it to be a much-shortened, .straight 

 species of Closterinm Cl. Nm-icula (Breb) Liitkem. but 

 there are equally good reasons for retaining the plant in the 

 genus Pi:'itiuin. 



Forma Willei Schmidle. 



1',-niitin Nttr'u-ula Breb. forma apidlus rotundato-truncatis. Wille, Norir 1 '* 

 Ft-rskv. Alg. 1880, p. 49, t. 2, f. 32 ; West, Alg. Eng. Lake Distr. 1892, 

 p. 721. 



P. Navicula forma Willei Schmidle, Lappmark Siisswasseralgen, 1898, 



p. 17. 



A form with the apices subtruncate. 



Length 41 // ; breadth 12 ,. 



ENGLAND. Bowness, Helvellyn, and Langdale, West- 

 moreland ! 



dpogr. Distribution. Germany. Switzerland. Aust- 

 rian Tyrol. Xorway. 



Var. crassum v<ir. nov. (PL VII, figs. 10, 17.) 



Cells about 3 times longer than their diameter, not 

 so attenuated ; apices very broad and rounded-truncate. 



Length 30-5-48 n( ; breadth 14* 5-1 5 '5^; breadth of 

 apices S'o-D'-j /<. 



