STAURASTEUM. 157 



Scott. Freslnv. Plankton, I. 1903, p. 529; Freshw. Alg. Orkneys & 

 Shetlands, 1905, p. 25 ; Further Contrib. Freshw. Plankton Scott. 

 Lochs, 1905, p. 486 ; Brit. Freshw. Phytoplankton, etc., 1909, p. 182. 



Semicells subtriangular, basal angles and apex 

 rounded, sides slightly convex ; cell-wall smooth. 



Zygospore globose, furnished with numerous, simple, 

 acute spines. 



Length 31-41 p.; breadth 22-36 /x ; breadth of 

 isthmus 7-11 /x ; diam. zygosp. without spines 36-40 //,, 

 with spines 60-06 /x. 



ENGLAND. - -Cumberland ! Westmoreland! Lan- 

 cashire! W., X., and E. Yorks ! Cheshire (Roy). 

 Leicestershire (Roy). Bucks ! Warwick (Wills). 

 Sussex ! Kent ! Hants ! Devon ! Cornwall ! 



WALES.- -General (but scarce) ! 



SCOTLAND. --General, and often conjugated (Roy $' 

 Bissett). Inverness ! Ayr ! Wigtown ! Lewis, Outer 

 Hebrides ! Orkneys ! Shetlands ! Rare in the plankton ! 



IE [ LAND. - -Donegal! Mayo (and Clare Island)! 

 Gal way ! Kerry! Dublin and Wicklow (Archer). 

 Down ! Londonderry ! 



Geoc/r. Distribution.- -France. Germany. Switzer- 

 land. Austria and Galicia. Hungary. Servia. Italy. 

 Portugal. Norway. Sweden. Denmark. Bornholm. 

 Finland. Poland. X., Central, and S. Russia. 

 Faeroes. Iceland. Nova Zembla. Spitsbergen. 

 Greenland. E. and N. India. Australia, United 

 States. Brazil. Bolivia. Paraguay. Argentina. 

 Patagonia, 



This is much the most abundant and widely distributed of 

 all the forms of St. orbicula/re, and one which has generally 

 been accepted as the type form. We have ourselves 

 invariably, although erroneously, recorded it as such. Its 

 most important character is the elevated apex of the semicell, 

 giving the latter a subtriangular outline. This variety and 

 var. extensum Nordst. are the only forms of St. orbicular e of 

 which the zygospores are known. 



A large form forma MAJOR [= St. orbiculare f. major West, 

 ' Alg. Engl. Lake Distr/ 1892, p. 731] is known from near 

 Bowuess, Westmoreland ; length 61 /.* ; breadth 50 /u ; breadth 

 of isthmus 17'5 /.<. 



