BBITISH DESMIDIACEJE. 



Var. Scoticum nob. (PL IX, fig. 18.) 



Cosmariiun Thwaitesii Ealfs, var. Scot ic urn West & Gr. S. West, New Brit. 

 Fresliw. Alg. 1894, p. 8, t. 1, f. 15 ; Roy & Biss. Scott. Desm. 1894, p. 

 256 ; Norclst. Index Desm. 18913, p. 255. 



Rather larger than the typical form, with the semi- 

 cells inflated. 



Length 95-97^; breadth 42 "5-43 -5 /< ; breadth of 

 constriction 3<3-37'5 /u. 



SCOTLAND. N"ew Galloway, Kirkcudbright ! 



Intermediate forms are sometimes met with between this 

 variety and the type. Such a form with slightly inflated 

 sides we have observed from Widdale Fell,, W. Yorks. (PI. IX 

 fig- 15). 



23. Penium crassiusculum De Bary. 



/ 



(PL VIII, figs. 4, 5.) 



PC i, I inn crassiusculum De Bary, Conj. 1858, p. 73, t. 5, f. 5-7; Cooke, Brit. 

 Desm. 188G, p. 44, t. 17, f. 7 ; Roy & Biss. Scott. Desm. 1894, p. 251 ; 

 Xordst. Index Desm. 1896, p. 86 ; Desm. Singapore, 1897, p. 157 ; West 

 & G-. S. West, Alga-fl. Yorks. 1900, p. 47 ; Alg. X. Ireland, 1902, p. 22. 



Cells rather small, 3-3 J times longer than their 

 diameter, cylindrical with parallel sides, with a distinct 

 median constriction, apices truncate with the angles 

 slightly rounded ; cell- wall smooth and colourless ; 

 chloroplasts with 4 or 5 somewhat irregular longitudinal 

 ridges. 



Zygospore "similar to that of P. phymatosporum, 

 but the angles less prominent and more rounded ' 

 (Roy). 



Length 57-70/t; breadth 20-23 /; breadth of 

 isthmus 18-18'5/t. 



EXGLAXD. Cowgill Wold Moss, Widdale Fell, W. 

 Yorks ! 



SCOTLAND. Not uncommon ; zygospore from Kyles 

 of Bute in Argyll (Roy $ Bisst'tt). Rhicoiiich, Suther- 

 land ! 



IKELAND. Xear Lough Glentornan, Donegal ! 

 Lough Fea, Londonderry ! Dublin and Wicklow 

 (Archer). 



