132 BRITISH DESMIDIACE^. 



4-, 5- or 6-angled, sides concave, centre of apex smooth, 

 angles produced to form short truncate processes. 



Zygospore large and spherical, with numerous appen- 

 dages twice dichotomous at the apex. 



Length 24-30 [JL ; breadth, including the processes, 

 16-48[x; breadth of isthmus 6-10^; diam. zygosp,, 

 without processes, 30 pt ; with processes, 50 ^ . 



ENGLAND. - - Cumberland ! Westmoreland ! (Rolfs). 

 Lancashire ! W. and N. Yorks. (up to 2000 feet) ! 

 Cheshire ; Leicester (Roy). Essex ! Warwicks (Wills). 

 Gloucester (Rolfs). Surrey (zygospores from Devil's 

 Jumps, Frensham Common) ! Sussex (Rolfs). Hants ! 

 (Roy). Devon ! (H orris). Cornwall! (Morquond). 



WALES. Abundant (at 2000 feet on Glyder Fach) ! 



SCOTLAND. General ! (Roy & Biss.). At 3500 feet 

 on Lochnagar, Aberdeen ! Orkneys ! Shetland? ! 



IRELAND. Donegal ! Mayo and Clare Isle ! Gal way ! 

 Kerry ! Dublin and Wicklow (Arch.). Antrim ! 

 Londonderry ! 



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

 Switzerland. Galicia and Austria. Hungary. Norway 

 and Finmark. Sweden. Finland. N. Russia. Spitz- 

 bergen. Greenland. Siberia (var.). Japan. India. Siam. 

 Java. Celebes. Tasmania. Azores (var.). Sandwich 

 Islands. United States. Brazil. 



St. margaritaceum occurs commonly in this country, and has 

 a very wide distribution. It is frequently found in association 

 with St. muricatum. Variations in connection with the granules 

 on the apex of the semicell are very common, and apart from 

 forms having the definite granulation of var. coronulatum or 

 var. fdbustum, specimens are not uncommon in which some of 

 the granules surrounding the apical smooth, area of the semicell 

 are very strongly developed, duplicated, or emarginate, so that 

 the apex of the cell in the front view is more complicated than 

 usual. 



Var. coronulatum West. (PL CL, fig. 10.) 



St. margaritaceum var. coronulatum West, Alg. N. Wales, 1890, p. 20, f. 3 ; 

 Liitkem, Desm. Millstattersees, 1900, p. 22 ; West & G. S. West, Alg. N. 

 Ireland, 1902, p. 57. 



