86 BRITISH DESMIDIACEJE. 



each side, and a pair of slightly divergent, minute 

 spines at the apical margin. Vertical view elliptic, 

 with one minute spine at each pole, and a small pro- 

 tuberance at the middle on each side. 



Zygospore unknown. 



Length without spines 11 '5 /*, with spines 12'5/x; 

 breadth without spines 12/x,, with spines 12* 5 p.; 

 breadth of isthmus 5 //, ; thickness 6*5 /x. 



IRELAND.- -In small lake near Recess, Galway ! 



This little species should be compared with X. concinnum 

 Arch., from which it differs in the form of its semicells and in 

 the pair of minute spines in the middle of the truncate apex. 



lo. Xanthidium concinnum Arch. 

 (PI. CXII, fig. 10.) 



Xanthidium concinnum Arch, in Ann. Mag. Nat. Hist. ser. 5, xi, 1883, p. _!S5 ; 



Cooke, Brit. Desm. 1887, p. 189; Nordst. Index De-sin. 1896, p. 78; 



W. & G. S. West, Alg. S. England, 1897, p. 484, t. 6, f. 15 ; Alga-fl. 



Yorks. 1900, p. 68 ; Freshw. Alg-. Orkneys and Shetlands, 1905, pT 23 ; 



Liitkem. Desm. Bohin. 1910, p. 497. 

 Arthrodesmus hexagonus Boldt, Siber. Chlorophy. 1885, p. 109, t. 5, f. 16 ; 



De Toni, Syll. Alg. 1889, p. 1059 ; Gutw. Flor. Glon. Okolic Lwowa, 



1891, p. 64, t. 3, f. 9; Eichler in Pamietnik fizyj. Akad. Umiej. Krakow, 



1894, p. 130. 

 Xanthidium hexagonum (Boldt) Turner, Freshw. Alg. E. India, 1893, 



p. 137. 



Cells minute, about as long as broad, deeply 011- 

 strictecl, sinus narrow and linear; semicells trans- 

 versely subhexao'onal with a broad, truncate (or very 



V O ' 



slightly convex) apex, lateral angles each furnished 

 with a single minute spine, apical angles each fur- 

 nished with a pair of minute spines, central area small. 

 Side view of semicell subcircular, with a small papilla 

 at the middle on each side and a pair of minute spines 

 at the apical margin. Vertical view elliptic, with a 

 prominent papilla at the middle on each side, with 

 one minute spine at each pole and a pair of minute 

 spines on each side near the poles. Chloroplasts axile, 

 with a single central pyrenoid in each semicell. 



Zygospore unknown. 



Length without spines 0-9*5 ft; breadth without 



