6 BRITISH DESMIDIACE^l. 



veiling incisions narrow, closed or slightly open ; polar 

 lobe smaller than the lateral lobes, convex and broadly 

 cnneate, with a deep and narrow median incision, from 

 vertical view oblong- elliptic with deeply emarginate 

 poles ; lateral lobes very broad, sides broadly hollowed 

 (sometimes with a rounded lateral projection), angles 

 rounded ; semicells with three prominent protuber- 

 ances across the base and two very slight tumours 

 across the middle. Side view of semicell subpyrami- 

 date, with subrectangular basal angles and a rounded- 

 truncate apex, the upper lateral lobule emarginate and 

 the lower one entire. Vertical view oblong-elliptic, 

 with a slight protuberance at each pole and one in the 

 centre of the convex sides. Cell-wall punctate, angles 

 of lobes strongly thickened. 



Zygospore unknown. 



Length 163-205 /x; breadth 79-106 /x; breadth of 

 isthmus 24-30 p, ; thickness 56-75 ^. 



ENGLAND. Cumberland ! Westmoreland ! (Ralfs). 

 W. and N. Yorks ! Lancashire ! Wilts ! Surrey ! 

 Sussex ! (Rolfs). Kent ! (Ralfs). Hants ! (Rolfs). 

 Devon! (Bennett). Cornwall. 



WALES. General in Carnarvonshire (Glyder Fach 

 at 2,200 ft.) ! Dolgelly, Merioneth ! 



SCOTLAND. General! (Roy $ Bissett). 



IRELAND. Donegal ! Mayo ! Galway ! Kerry ! 

 Dublin and Wicklow (Archer). Down ! 



Geogr. Distribution. - France. Germany. Galicia 

 in Austria. Italy. Norway. Sweden. Denmark. 

 Finland. Poland. Faeroes. India. United States. 



E. craasum is a large and handsome species which occurs 

 abundantly in many parts of the British Isles, and it is rather 

 remarkable that up to the present time its zygospores have 

 escaped observation. 



It is a somewhat variable species with regard to the incisions 

 between the lobes and the form of the lateral lobes. The 

 interlobular incisions may be narrow and closed, or they may 

 be considerably open, and the lateral lobes frequently possess 

 a median rounded protuberance. This is a variation which 

 has received a name from several authors ("var. appendicu- 



