PENIOI. S ( .) 



subcylindrical, with a slight median constriction, 

 gradually attenuated towards the apices, which arc 

 rounded or truncately rounded and sometimes dilated ; 

 transverse sutures usually several or many (10 have 

 been observed), marking the junction of cylindrical 

 interpolated pieces of cell-wall of various ages ; cell- 

 \vall pale yellow or yellow-brown in colour, furnished 

 with longitudinal striae which have a variable spiral 

 twist ; striae sometimes anastomosing or often partly 

 replaced by rows of dots ; between the striae finely 

 punctate. 



Zygospore globose and smooth. 



Length 123-274 ,* ; breadth 20-26 n ; breadth of 

 apices 13' 5 16 /<. 



ENGLAND. Cumberland ! Westmoreland ! W. and 

 N. Yorks ! Lancashire ! Surrey ! Cornwall ! 



WALES. General in Carnarvonshire ! Ffestiniog, 

 Merioneth ! 



SCOTLAND. Eoss, Inverness! , Aberdeen, Kincardine, 

 Perth!, Dumbarton, Argyll (Roy $ Bissett). Suther- 

 land ! Lewis and Harris, Outer Hebrides ! 



IRELAND. General in Mayo ! Galway ! Kerry ! 

 Donegal ! Armagh ! Down ! 



Geoijr. Distribution. France. Germany. Austria. 

 Hungary. Portugal. Denmark. Norway. Sweden. 

 Finland. Ceylon. Java. United States. 



The structure of the cell-wall of this Desmid lias been care- 

 fully investigated (vide CI. S. West, Variation Desm. 1899, 

 pp. 377-380) and its striolation has been shown to be its 

 most variable character. The stride may be coarse, fine, or 

 broken up into series of dots, even in different individuals 

 from the same gathering, thus exhibiting the main characters 

 of the three forms described by Turner as Penium #]>ii-t>*- 

 triolatum, P. Royanum, and P. scandinavicum. The number 

 seen at one time across the cell varies from about 8 to 

 13, and this variation may be seen on one individual,, the 

 striolations being more crowded at some parts of the cell- 

 wall than at others. In one individual two striolations were 

 observed to be 2'3 /LI apart, and the distance between one of 

 these and the next one was 5'2 ja. They are generally 

 arranged around the cell in a spiral manner from apex to 



