MICRASTERIAS. 103 



bidentate (rarely tridentate) parts. Side view of 

 semicell ovate-lanceolate, with a broadly truncate 

 apex and an inflated base. Vertical view narrowly 

 elliptic -rhomboid, with acute poles and a small in- 

 flation in the middle of each side. Cell-wall delicately 

 punctate. 



Zygospore globose, furnished with many strong, 

 elongate, simple spines. 



Length 208-366 /*; breadth 165-305 p.; breadth of 

 isthmus 29-43 ^ ; breadth (maximum) of polar lobe 

 48-80 jit ; diam. zygospore without spines 108 IJL, with 

 spines 158 p.. 



ENGLAND. Cumberland ! Westmoreland (up to 

 2,400 ft, on Helvellyn) ! (Balfi). W. and K Yorks ! 

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

 Gloucestershire (Balfs). Wilts ! Surrey ! (Rolfs). 

 Sussex (Balfs). Kent ! (Balfs). Hants ! (Bennett). 

 Devon! (Bennett). Cornwall! (Balfs). 



WALES. Capel Curig! (Cooke $ Wills), Llyn Padarn! 

 Llyn Idwal !, T Foel Fras !, Carnarvonshire. Glamor- 

 ganshire ! 



SCOTLAND. General ! Zygospores from Slewdrum, 

 Aberdeen ; near Bishop's Dam, Kincardine ; Monroman 

 Moor, Forfar (Boy fy Bissett). Occasional in the 

 plankton ! Outer Hebrides ! Shetlands ! 



IRELAND. General, but scarce ! Zygospores from 

 Wicklow (Archer). 



Geogr. Distribution. France. Germany. Austria. 



Galicia. Hunsfary. Italv. Norway. Sweden. Den- 



~ / / i/ 



mark. Bornholm. Finland. Poland. S. and Central 

 Russia. Japan. India. Siam. Singapore. United 

 States. Brazil. 



M. rotata is not a common species, although very widely 

 distributed. It is easily distinguished from M. denticulata 

 by the emarginate-dentate lobules and by the polar lobe, which 

 is slightly exserted and furnished with bidentate angles. 



The principal variation is in the polar lobe, especially 

 in the amount of its exsertion. Sometimes the incisions 

 on each side of the polar lobe are more or less open, and 



