92 BRITISH PESMIDIACE/E. 



truncately rounded ; cell- wall with very delicate longi- 

 tudinal striolations ; chloroplasts with one pyrenoid. 



Zygospore subquadrate or rectangular, with the 

 angles obtuse and protruding ; apices and sides con- 

 cave, w r ith a rounded protuberance on each side and 

 four similar ones within the angles ; side view of 

 zygospore sexangular ; cell-wall thick. 



Length 20-42 /*; breadth 11-18^; length of zygosp. 

 36-42 /i ; breadth of zygosp. 30-36 /i. 



ENGLAND. Minety, Wilts (with zygospores ; Joslnm). 



SCOTLAND. Near Mill of Muchalls, Kincardine (with 

 zygospores; Eoij Bissett}. 



IRELAND. Dublin and Wicklow (Archer}. 



Georjr. Distribution. France. Austria. Italy. Argen- 

 tina. Trinidad (?). 



This species is characterised by its delicately striated cells 

 and its peculiar zygospore. 



19. Penium subtile West & G. S. West. 

 (PL VIII, figs. 27-29.) 



Penium suUile West & G. S. West, Alg. S. England, 1897, p. 479, t. 6, 

 f. 8, 9. 



Cells very minute, almost 1-| times longer than their 

 diameter, ellipsoid with a very faint median constric- 

 tion (often only indicated by a median suture), apices 

 subtruncate ; cell-w^all colourless, very delicately and 

 indistinctly punctulate ; punctulations scattered, about 

 12 in each semicell ; chloroplasts with one pyrenoid, 

 and with two, three, or four longitudinal ridges ; some- 

 times with only one chloroplast situated in the median 

 portion of the cell. 



Zygospore unknown. 



Length 14-15 /; breadth 10-11 /u. 



ENGLAND. -Thursley Common, Surrey! 



WALES.' Llyn Geirionedd, Carnarvonshire ! 



SCOTLAND. Near Balallan, Lewis ; and a pure 

 gathering from S. Harris, Outer Hebrides ! 



This is a rare species which occasionally occurs in pro- 



