4 BRITISH DESMIDIACE.E. 



1. Euastrum ventricosum Lund. 

 (PL XXXIII, figs. 1-3.) 



? Euastrum crassum (Breb.) Kiitz. var. /3 Kalfs, Brit. Desm. 1843, t. 11, 



f. 3e,/. 

 Euastrum ventricosum Lund. Desm. Suec. 1S71, p. 18, t. 2, f . 2 ; Wolle, 



Desm. U.S. 1884, p. 160 ; Cooke, Brit. Desm. 1886, p. 67, t, 33, f. 1 ; 



Wolle, Freshw. Alg. U.S. 1887, p. 38, t. 58, f. 1-3 ; De Toni, Syll. Alg. 



1889, p. 1090; West, Alg. N. Wales, 1890, p. 287; Alg. W. Ireland, 



1892, p. 137 ; Roy & Biss. Scott. Desm. 1893, p. 178 ; Nordst, Index 



Desm. 1896, p. 267 ; West & G. S. West, Alg. S. England, 1897, p. 483 ; 



Alg. N. Ireland, 1902, p. 28. 

 Helierella ventricosa Kuntze, Kevis. gen. plant. 1891, p. 899. 



Cells rather above the medium size, 1^ times longer 

 than broad, deeply constricted, sinus narrowly linear ; 

 semicells in front view somewhat semi-elliptical, strongly 

 dilated at the base, unequally three-lobed, the inter- 

 vening incisions narrow ; polar lobe smaller than lateral 

 lobes, strongly convex, with a deep and narrow median 

 incision, from vertical view oblong- elliptic with deeply 

 emarginate poles ; lateral lobes bilobulate, with a broad 

 median hollow, upper lobule obtuse and from the side 

 view entire, lower lobule subtriangular with basal angles 

 somewhat rounded; semicells with three tumours across 

 the base and two across the middle. Side view of semi- 

 cell somewhat pyramidate, with a protuberance on each 

 side below the middle ; apex dilated, truncate, with 

 rounded angles. Vertical view angular-elliptic, showing- 

 five undulations on each side. Cell- wall punctate. 



Zygospore globose, furnished with large pointed 

 teeth which are mostly curved (about twelve teeth 

 visible around the margin). 



Length 80-136 ^ ; breadth 52-80 /x ; breadth of 

 isthmus 18-28 /A; thickness 33-48 /i; cliam. zygosp., 

 with teeth, about 110 p.. 



ENGLAND. Near Bowness, Westmoreland (Bissetfy. 

 Hawkshead, Lancashire ! Thursley Common, Surrey ! 

 Near Bovey Tracey, Devon (Bennett). 



WALES. Llyn Teyrn, Snowdon, bog above Capel 

 Curio; Lakes, Carnarvonshire ! Dolg;elly, Merioneth ! 



o O */ 



SCOTLAND. Sutherland Inverness ! Aberdeen ! 



