XANTE I DI I'M. 85 



subrectangular, with convex lower margin, subparallel 

 sides, and a slightly convex apex, or subpyramidate- 

 trapeziform, Avith broadly rounded basal angles, and 

 almost straight sides and apex ; spines very minute, 

 1-2 at each superior angle and 1-4 at the margin of 

 each basal angle, within the margins and towards the 

 centre with a few irregularly disposed spines (or acute 

 granules) ; central area protuberant but not thickened 

 or granulate. Vertical view elliptic, with a small 

 rounded protuberance at the middle on each side, 

 poles rounded, each polar margin furnished with 3-(> 

 minute spines. 



Zygospore unknown. 



Length without spines 18-2 7 ft; breadth without 

 spines 1(3-24 />t; length of spines 0*8-1*2 p.; breadth of 

 isthmus 5*5-9*7 {JL; thickness 11*5-13 /x. 



SCOTLAND. Orknevs ! 



t/ 



AVe have only observed tins small species from a Sphagnum- 

 hog* in the Orkney Islands, and in 1896 gave a description 

 of it under the name of X. Robinsonianum. We now know 

 that our identification was incorrect, and we therefore 

 describe ir as a new species. X. Orcadense differs from 

 X. Robinsonianum in its open sinus, in its more scattered and 

 more reduced spines, and in the rounded and less evident 

 central protuberance. 



14. Xanthidium apiculiferum AVest. 

 (PI. CXIII, fig. 9.) 



X, i a th'ul. linn vpicii.li/e'nnn West, Alg-. W. Ireland, 1892, p. 167, t. 2-1, f. 17; 

 Xordst. Index Desin. 1896, p. 48. 



Cells minute, as long as broad, deeply constricted, 

 sinus narrow and slightly open ; semicells very 

 broadly pyramida te-trapezif orm, angles slightly rounded 

 and apex broadly truncate, inferior angles each fur- 

 nished with a single minute spine, superior angles each 

 furnished with a pair of minute spines, and with a 

 similar pair in the middle of the apex, central area 

 small and protuberant. Side view of semicell sub- 

 circular, with a small protuberance at the middle on 



