X ANT HID HTM." 83 



Griitwinski, with his customary lack of perception, has seized 

 upon ifc as a reason for naming the British specimens X. 

 Westianum ! 



12. Xanthidium Robinsonianum Arch. 

 (PL CXIII, figs. 10-12; PL CXVIII, figs. 1-3.) 



X < i titliidium Robinsonianum Arch, in Q. J. Micr. Sci. N.S. xxii, 1880, 

 pp. 114, 116; Joshua in Journ. Bot. xxi, 1883, p. 291; Wittr. & 

 Nordst. Alg. Exsic. 1883, no. 550 ; Cooke, Brit. Desm. 1887, p. 134 ; 

 De Toni, Syll. Alg. 1889, p. 924. 



X. vat-while (Nordst.) W. & GK S. West var. comvlexuni W. & G-. S. West, 

 Alg-. N. Ireland, 1902, p. 31, t. 2, f . 8. 



Cells small, as long as broad, deeply constricted, 

 sinus narrowly linear with a slightly dilated extremity; 

 semicells widely pyramidate-trapeziform, apex straight 

 or very faintly retuse, upper parts of sides slightly 

 retnse, apical angles slightly rounded, basal angles 

 broadly rounded ; spines minute, variable in number 

 and exact disposition, but mostly grouped at the 

 angles and within the margin of the semicells, 2-4 at 

 each angle and with groups of 2-3 within the margins, 

 one of these groups almost invariably situated just 

 below the middle of the apex ; central area small and 

 protuberant, furnished with 3-5 granules more or less 

 irregularly disposed and sometimes connected by other 

 acute granules with the small group of spines below 

 the apex. Side view of semicell depressed-circular, 

 with an emarginate protuberance on each side. Ver- 

 tical view elliptic, with an emarginate protuberance at 

 the middle on each side, poles rounded and furnished 

 with 5-8 minute spines. 



Zygospore globose, furnished with " delicately 

 furcate, tuberculose" spines (Joshua). 



Length without spines 22-25 /x, with spines 24- 

 26*5 ju,; breadth without spines 22-25 /x, with spines 

 24-28 /A; breadth of isthmus 6'5-8'5/^; thickness 

 14'5-16 ft. 



WALES. Boo- between Grlyder Fach and the river 



O f/ 



Llugwy, Carnarvonshire ! 



SCOTLAND. N. of Barvas, Lewis, Outer Hebrides ! 



