126 BKITISH DESMIDIACE^E. 



1892, p. 30 ; West, Alg. W. Ireland, 1892, p. 181 ; Roy & Biss. Scott. 

 Desm. 1893, p. 23 ; Liitkem. Desm. Attersees, 1893, p. 567 ; W. & G. S. 

 West, Alg. S. England, 1897, p. 495 ; Borge, Siisswasseralgen Franz 

 Josefs Land, 1899, p. 763 ; Comere, Desm. de France, 1901, p. 157, t. 13, 

 f. 13 ; West & G. S. West, Alga-fl. Yorks. 1902, p. 105 ; Freshw. Alg. 

 Orkneys and Shetlands, 1905, p. 26 ; Gutw. Flor. Alg. Mont. Tatrensium, 

 1909, p. 475; Georgev., Desm. Macedon. 1910,' p. 244; Hustedt, Desm. 

 Tirol, 1911, p. 340. 



Didymidium (Staurastrum) polymorphum Reinsch, Algenfl. Frank. 1867, 

 p. 165 (in part). 



Cells small, about Ij times broader than long, includ- 

 ing the processes, constriction moderately deep, sinus 

 acute and almost rectangular, sometimes minutely 

 acuminate at its apex ; semicells variable in form, 

 subelliptical, subfusiform or even subcuneate, ventral 

 margin usually more strongly convex than the dorsal ; 

 semicells attenuated at the angles to form short stout 

 processes, horizontal or very slightly incurved, tipped 

 with 3 or 4 minute spines and provided with 3 or 4 series 

 of minute denticulations ; ' body : of semicell also 

 granulate, granules arranged in concentric series round 

 the angles. Vertical view usually 3- (-7-) angular, the 

 two semicells of the same individual often differing in the 

 number of processes, lateral margins very slightly con- 

 cave ; centre of apex smooth. Chloroplast axile, with 

 a central pyrenoid in each semicell, and a pair of lobes 

 extending into each angle. 



Zygospore spherical or somewhat angular, with stout 

 processes, branched at the apex. 



Length 21-29 [L ; breadth, including processes, 21- 

 43 (X ; breadth of isthmus 6-8 ^ ; diam. zygosp., without 

 processes, 30 (JL ; including processes, 55 pi. 



ENGLAND. Cumberland ! and in the plankton of 

 Ennerdale Water ! Westmoreland (Bissett) ! Lancashire 

 (Roy). W., N., and E. Yorks! Cheshire (Roy). Leicester 

 (Roy). Essex! Warwicks (Wills) !, and in the plankton 

 of Bracebridge Pool, Button Park ! Worcester (Griffiths) ! 

 Surrey ! Sussex (Rolfs}. Hants (Bennett) \ Dartmoor, 

 Devon (Harris). Cornwall ! (Marquand). 



WALES.- -Bethesda, Llyn Idwal, Snowdon, Capel 

 Curig, Llyn Bochlwyd, Moel Siabod, and Llyn-y-cwm- 



