40 BRITISH DESMIDIACE.E. 



sides; lower lobule subrectangular, sometimes emar- 

 ginate, and furnished with two or three sharp granules ; 

 upper lobule rounded or rounded-truncate, rarely 

 emarginate, sometimes furnished with one or with two 

 sharp granules ; apex convex, sometimes slightly 

 undulate, with a deep median notch, which may be 

 somewhat open or closed, with a short, blunt spine at 

 each apical angle, and usually with a thickening at the 

 angles on each side of the apical incision; semicells 

 with a granulated protuberance in the centre above 

 the isthmus (number and disposition of granules vari- 

 able), with a large granule below and on each side of 

 the apical incision (sometimes absent), and with a few 

 variously-disposed granules within the lateral lobules 

 and the apex. Side view of semicell ovate, with a 

 protuberance (usually emarginate) on each side near 

 the base, and a granule on each side higher up on the 

 lateral margins ; apex rounded and tridenticulate. 

 Vertical view elliptic, with a protuberance (emarginate 

 or trigranulate) at the middle on each side, poles 

 furnished with acute granules or denticulations. 



Zygospore globose, furnished with numerous strong 

 simple spines, most of which are curved. 



Length 51-61 ju; breadth 32-39 p ; breadth of apex 

 25-29 /x; breadth of isthmus 6*3-11 /LI ; thickness 

 21-23 /A; diam. of zygosp. without spines 40-42*5 /u,; 

 length of spines 10-13 p,. 



ENGLAND. Westmoreland ! N. and W. Yorks ! 

 Lancashire ! Essex ! Oxfordshire ! Surrey ! Kent ! 

 Hants, (zygospores from the New Forest) ! Devon ! 

 Cornwall ! 



WALES. General throughout Carnarvonshire (at 

 2,200 ft. on Glyder Fach) ! 



SCOTLAND. Common ! (Roy $ Bissett). Outer 

 Hebrides ! Orkneys ! Shetlands ! 



IRELAND. General ! 



Geogr. Distribution. Germany. Norway. Sweden. 

 Denmark. Bornholm. Iceland. Greenland. Russia. 

 United States. Brazil. 



