272 BRITISH DESMIDIACEjE. 



Leicestershire (Roy). Essex ! Cambridgeshire ! 

 Gloucestershire (Rolfs). Surrey! (Rolfs). Sussex! 

 (Ralfx). Kent! Hants ! (Roy). Devon! Cornwall! 

 (Rolfs). 



WALES.- -General in Carnarvonshire and Merioneth ! 

 Anglesey ! 



SCOTLAND. General! (Ray $ Bissett). Orkneys! 

 Shetlands ! Very common in the Outer Hebrides ! 



IRELAND. --General ! Rare in plankton of Lough 

 Corrib, Galway ! 



Geogr. Distribution.- -France. Belgium. Germany. 

 Austria and Galicia. Bosnia. Hungary. Italy. 

 Switzerland. Norway. Sweden. Bornholm. Poland. 

 Finland. Russian Lapland. N. Russia. Faeroes. 

 Iceland. Spitzbergen. Greenland. Mongolia. China. 

 Japan. India. New Zealand. Azores. United States. 

 Brazil. Patagonia. 



C. tetraopJithalmum is found generally distributed over the 

 whole of the British Islands, but move especially in Sphagnum- 

 bogs and in peaty moorland ditches. It often occurs in 

 quantity associated with Xanthidium armatum, Tetmemorus 

 granulatus, Gymnozyga moniliformis, Micrasterias denticnlata, 

 M. truncata, Euastrum Didelta, etc. In both England and 

 Wales it is a fairly common bog-species, but it reaches its 

 maximum abundance in some of the boggy pools of the 

 North-west of Scotland and the West of Ireland. 



The figures of this Desmid given by Ralfs are not very 

 accurate, and those of Delponte and Cooke are equally bad. 

 We first pointed this out in the Journ. Roy. Microscop. Soc. 

 1890, p. 289. The granulation is most inaccurately figured, 

 and the centre and apices are depicted as coarsely granulate 

 like the rest of the semicell, which is never the case. We 

 have examined hundreds of specimens of this species from all 

 parts of the British Islands, including all those localities from 

 which Ralfs (and, through the latter, Brebisson) obtained it, 

 and we have never yet seen a specimen in which the granules 

 were not greatly reduced both in the centre and at the apices 

 of the semicells. Thus, the only form observed by Luudell in 

 Sweden, and subsequently named by Wittrock as " var. 

 Lundellii" is the common form throughout the whole of the 

 British Islands, and undoubtedly the one which both Ralfs 

 and Brebisson examined at the time the characters of the 



