XANTHIDIUM. 01 



This distinctive variety occurred abundantly in Locli Sliin, 

 and we suggested at the time of its description that owing to 

 its striking characters it might perhaps be regarded as a 

 distinct species X. planet onicum. 



The cells are larger than those of the type, the sinus is 

 closed, the spines are longer, and those of the inferior angles 

 are less divergent; in the centre of the semicells is a scro- 

 biculated area which is thickened and possesses a small pro- 

 tuberance clearlv visible in the vertical and lateral views. 

 As in typical X. controversum, single spines are frequently 

 replaced by a pair. 



It should be compared with X. tetracaiithum Turner 

 ('Freshw. Alg. E. India/ 1893, p. 101, t. 13, f. 29), from 

 which it differs in its hexagonal semicells, closed sinus, and 

 longer spines. 



5. Xanthidium Smithii Arcli. 

 (PL CVIII, figs. 1-4; PL CXI, fig. 10.) 



Xanthidium Smithii Arch, in Proc. Dubl. Nat. Hist. Soc. iii, 1860, p. 51 > 

 t. i, f. 10-12; in Q. J. Micr. Sci. 1860, p. 238, t. 11 ; in Pritch. Infus. 

 1861, p. 736; Eabenh. Flor. Europ. Alg. Ill, 1868, p. 224; Cooke, 

 Brit. Desin. 1887, p. 133, t. 45, f . 4 ; West, Alg. W. Ireland, 1892, p. 

 166 ; Roy & Biss. Scott. Desm. 1893, p. 245 ; W. & G. S. West, Notes 

 Alg. Ill, 1903, p. 74. 



Arthrodesmus octocornis Ehr. var. -major Roy & Biss. Scott. Desm. 1894, 

 t. 2, f. 20 [not KaltV. 



Cells small, deeply constricted, sinus open and 

 acute-angled with a rounded apex ; semicells rect- 

 angular-trapeziform, basal and apical angles rounded, 

 sides and apex very slightly concave (or almost 

 straight), each angle furnished with a pair of simple, 

 straight, and fairly long spines, with a small thickened 

 area in the centre of the semicell. Side view of semi- 

 cell circular, with a small protuberance at the middle 

 on each side, and with a pair of diverging spines at 

 the apex. Vertical view elliptic-rhomboid, with a 

 small rounded protuberance at the middle on each 

 side, and with a pair of diverging spines at each pole. 

 Chloroplasts ? 



Zygospore globose, furnished with long, simple, 

 acute spines (about 7 visible at the actual margin), 

 each arising from a widely conical base. 



