120 BRITISH DESMIDIACEJ1. 



margin not tumid, gradually but slightly attenuated 

 from the middle to each extremity ; apices truncately 

 rounded or sometimes rounded, often slightly swollen 

 and sul (capitate ; cell-wall reddish-brown in colour, 

 generally darker at the apices, costate, with 4 costae 

 visible across the cell, costse frequently subspirallv 

 disposed; each chloroplast with 4-7 pyrenoids in 

 one axile series; terminal vacuoles with a number 

 (12-20) of moving granules. 



Zygospore unknown. 



Distance between apices (= length) 290-40:3 p. ; 

 breadth 16-28 p; breadth of apices 12 15 /A. 



ENGLAND. Westmoreland! (linlfx). W. and N. 

 Yorks (very scarce)! Lancashire! Sussex (Half*). 

 Surrey! (Bait's). Hants! (Beinirtt). Devon! (Bennett). 

 Cornwall ! (Marqitand). 



WALES. Capel Curig! (Cuuke $ Wills), Pen-y- 

 gwryd (jRo//), Glyder Fach (at 2,200 ft.), Carnarvon- 

 shire ! Ffestiniog and Dolgelly, Merioneth ! 



SCOTLAND. Sutherland ! , Ross ! , Inverness ! , Aber- 

 deen ! , Kincardine, Forfar, Perth ! , Stirling, Argyll, 

 Renfrew (Hoi/ ^ Bissett). Kirkcudbright! Lewis and 

 Harris, Outer Hebrides ! 



IRELAND. Mayo ! Galway ! Kerry ! Donegal ! 

 Dublin and Wicklow (Archer). 



Geogr. Distribution. France. Germany. Austria. 

 Italy. Norway. Sweden. Denmark. Lapland 

 in Russia. India. Java. United States. 



This is a most characteristic species by reason of the few 

 strong costge on the cell-wall. It exhibits much yariation 

 with regard to its extremities, the poles being truncate, 

 rounded, or even suhcapitate, and the costas are frequently 

 disposed in a subspiral manner. The forms most frequently 

 met with in the British Islands possess sliglitly swollen ex- 

 tremities. 



8. Closterium costatum Corda. 

 (PL XIII, figs. 1-3.) 



Closterium costatum Corda, in Aim. de Carlsbad, 1834, p. 185, etc., t. 5 

 f. (51-63 ; Ealfs, Brit. Desm. 1848, p. 170, t. 21, f. 1 ; Arch, in Pritcli. 



