STAUKASTUL'M. 171 



Zygospore globose, and " furnished with spines 

 forked at the apex' (Ralfs). 



Length 2:2-00 /x; breadth 21-ol/x; breadth of 

 isthmus 7'o-lK") p.. 



ENGLAND.- -Cumberland ! Westmoreland ! (Raff*). 

 "W., X.,andE. Yorks ! Leicestershire (Roy). Essex ! 

 Oxfordshire ! Gloucestershire ! Surrey (zygospores 



from Thurslev Common) ! Sussex ! Kent ! Hants ! 







Devon ! Cornwall ! 



WALKS.- -Llyn Padarn !, Moelfre !, Capel Curig ! 

 (Coolie $ TF//Zx), and Bettwys-y-Coed (Roy), Carnar- 

 vonshire. Llvii Coron, Anglesey ! Dolo;ellv, Merio- 



/ O / O e/ 



neth (Rolfs)* 



SCOTLAND. --Sutherland !, Ross, Inverness, Aberdeen, 

 Kincardine, Forfar, Perth !, Fife (Roy $ Bissett). 



Cumbra?, Ayr ! Lewis, Outer Hebrides ! Plankton of 

 i 



Loch Asta, Shetlands ! 



IRELAND. Donegal ! Mayo ! Gal way ! Kerry ! 



O I/ tJ V 



Dublin and Wicklow (Archer). Londonderry! 



Geor/r. Distribution.- -France. Germany. Austria 

 and Galicia. Servia. Italy. Norway (and Finmark). 

 Sweden. Denmark. Bornholm. Finland. X. Russia. 

 Faeroes. Iceland. Xova Zembla. Greenland. India. 

 Siam. Australia. Xew Zealand. Central Africa. 

 United States. 



Staurastrum alternans is a characteristic species with a 

 world-wide distribution. It is found in all parts of the 

 British Islands, but is never common. When seen in exact 

 front view the semicells are narrowly elliptic-oblong'., although 

 the slightest tilting to an oblique position at once causes a 

 change in their form. This fact alone is sufficient to separate 

 St. alternans from St. punctulatum, although there are other 

 important differences, such as the proportionately shorter 

 cells, less open sinus, more rounded angles, and more retnse 

 sides in the vertical view. 



Ralfs' figure of St. alternans is very poor, scarcely 

 differing in any respect from his figure of St. dilatatnm except 

 that it is triangular in vertical view. We have given a copy 

 of this figure (PL CXXYI, fig. 9), although it conveys little 

 idea of the characters of the species. 



The granules in this species are only definitely arranged 



