Z BRITISH DESMIDIACE.E. 



Cosmarium Botrytis var. interstitiale Kutz. Spec. Alg. 1849, p. 175. 

 Euastrum (Cosmarium) Botrytis Nag. Gatt. einzell. Alg. 1849, p. 119, t. 



7A, f. 3 ; Gay, Monogr. loc. Conj. Montpellier, 1884, p. 63. 

 Didymidium (Cosmarium) Botrytis Eeinsch, Algenfl. Frank. 1867, p. 120 



[in part]. 

 ? Cosmarium Botrytis var. pseudospeciosa Istvanffi, Diag. prsev. Alg. nov. 



Hungar. 1887, p. 236. 

 Ursinella Botrytis Kxmtze, Eevis. gen. plant. 1891, p. 923. [Vide Nordst. 



in Hedwigia, 1893, p. 152.] 



Cells above medium size, about 1 J-l J times as long 

 as broad, deeply constricted, sinus narrowly linear with 

 a dilated extremity; semicells ovate-pyramidate from 

 a broad, flat base, basal angles rounded, sides convex, 

 apex rather narrowly truncate or subtruncate, apical 

 angles rounded. Side view of semicell broadly elliptic. 

 Vertical view elliptic, ratio of axes about 1 : 1*8. 

 Cell-wall uniformly granulate, granules somewhat 

 small and generally without any definite disposition 

 (sometimes with a slight indication of a concentric 

 arrangement or even a disposition in decussating 

 oblique series), about 30-36 visible at the margin of 

 the semicell. Chloroplasts axile, with two pyrenoids 

 in each semicell. 



Zygospore globose, furnished with short, stout 

 processes, 3 (rarely 4) -fid at the apices, and generally 

 arising from broad, expanded bases. 



Length 65-90 /z; breadth 51-68 JJL; breadth of 

 isthmus 17-24/z; thickness 33-40 ju,; diam. zygosp. 

 without processes 5466 /x, with processes 69-84 /z. 



ENGLAND.- -Cumberland ! Westmoreland ! (Rolfs). 

 Lancashire ! W., N., and E. Yorks. (zygospores from 

 Markington and Pilmoor) ! Cheshire (Roy). Leices- 

 tershire (Roy). Lincolnshire ! Norfolk ! Suffolk ! 

 Essex! (Ralfs). Cambridgeshire! Warwickshire! 

 (Wills). Worcestershire! Gloucester! (Ralfs). Mid- 

 dlesex (zygospores from Harefield) ! Surrey (zygo- 

 spores from Frensham Great Pond) ! Sussex (Ralfs). 

 Kent! Hants! Wilts! Devon! (Bennett). Corn- 

 wall ! (Ralfs). JSTot uncommon in the plankton ! 



WALES. General ! Frequent in the plankton ! 



SCOTLAND. - -General ! Zygospores from Loch Kin- 



