XAXTHIDIUM. 53 



4 in each semicell, each with several pyrenoids; but 

 frequently variable (?). 



Zygospore globose or subgiobose, thick-walled, and 

 rather densely covered with large scrobiculations. 



Length (with spines) 116-185 ^ ; breadth (with 

 spines) 78-127 /x; breadth of isthmus 30-43 p. ; thick- 

 ness 0388 jji ; diam. zygosp. 100-131 ^. 



ENGLAND.- -Cumberland ! Westmoreland! Lanca- 

 shire ! W. and N. Yorks ! Norfolk (Coole). Herts 

 (IJfOtfU'fll). Bucks! Warwickshire (Wills). Surrey ! 

 fSussex ! Kent! Hants! Devon! (Bennett). Corn- 

 wall! (Ralfii). In the plankton of Codale and Easdale 

 Tarns, Westmoreland ! 



WALES.- -General! Zygospores from Capel Curig, 

 Carnarvonshire (Roy). Not uncommon in the plank- 

 ton. 



SCOT i, AND.- -Greneral ! Zygospores from Loch Inver, 

 Sutherland; Cammie, Kincardine; and Glencoe, Argyll 

 (Roy <J* Bissett). Lewis, Harris, N. and S. Uist, and 

 Benbecula, Outer Hebrides ! Greneral in the plankton 

 of the western lochs ! Zygospores in abundance from 

 boo; near Loch Coruisk, Skve ! 



CD y / 



I UK LAND.- -Donegal ! Mayo ! Gal way Kerry 

 Dublin and Wicklow (Archer). Down ! Very rare in 

 the plankton of the lakes in Galway ! 



Geoyr. Distribution. France. Germany. Austria 

 and Galicia. Huno-ary. Italv. Norway. Sweden 



O /' e/ v 



(with zygospores). Denmark. Finland. Poland. 

 N. and S. Russia. Faeroes. N. India. New Zealand 

 (var.). Cuba. United States. 



X. ar mat win is generally distributed over the Avhole of the 

 British Islands except the eastern counties of England. It 

 often occurs in abundance in Sphagnum-hogs and at the 

 "boggy margins of lakes. It also occurs in both the plankton 

 and benthos of the lakes of the western British areas, being 

 associated with various species of Gotsmarium } Staurastrum, 

 Micrasterias, and Euastrum, and with the filamentous genera 

 Gymnozyga and Hyalotheca. 



One of the handsomest of Desmids, X. armatum is the only 

 British species which possesses furcate spines. Six series of 



