XANTHIDIUM. 63 



IRELAND,- -Cromagloun, Kerry ! 



Geogr. Distribution. --Norway. Sweden. Poland. 



This variety is not quite so rare as the type, but is very local 

 and confined to the rich bogs of the old formations. It is 

 easily distinguished by its stouter habit and thicker spines, 

 which are somewhat variable. Two is the usual number 

 at each angle of the semicell, but the basal angles are fre- 

 quently furnished with three, and more rarely with only one. 



It seems to us an error of judgment to place this variety 

 under Arthrodesmus octocornis notwithstanding' the fact that 

 the semicells are identical in outward form. The spines are 

 usually in pairs, and the vertical view shows that the central 

 area of the semicell is very slightly thickened. The association 

 of these characters is clear evidence that this plant should be 

 placed in the genus Xantliidium. 



There seems little doubt that the Desmid described by 

 Reinsch as Xantliidium bicornutum should be relegated to 

 this variety. It might be regarded as : 



Forma MINOR [ = Xanthidium bicornutum Reinsch, Spec. 

 Gen. Alg. 1867, p. 119, t, 20 A III, f. 1-6; Didymidium 

 (Kantlridium) bicornutum Reinsch, Algenfi. Frank. 1867, p. 

 128, t. 9, f. 7; Arthrodesmus ? bicornutum De Toni, Syll. Alg. 

 1889, p. 1064]. 



Var. collum West. (PI. CVIII, fig. (3.) 



X. Smithii var. collum West. Alg. W. Ireland, 1892, p. 166, t. 22, f. 5. 



Each superior angle of the semicell with three 

 spines ; isthmus elongated so that the sinus is wide 

 and rounded- quadrate ; central protuberance of semi- 

 cell rather prominent and a little irregular. 



Length without spines 30 ju, ; breadth without spines 

 25 ju,; breadth of isthmus 9 p,; thickness 15 //,; length 

 of spines 5 7 '5 p.. 



IRELAND. --Cromagloun, Kerry ! 



6. Xanthidium antilopseum (Breb.) Kiitz. 

 (PL CVIII, figs. 7-18.) 



? Xanthidium fasciculatum Ehrenb. var. polygonum Ehrenb. Infus. 1838, 

 p, 148, t. 10, f. 24a [description and figure imperfect]. 



Heterocarpella antilopsea Breb. in Cheval. Des. microscop. et de letir usage, 

 Paris, 1839, p. 272. 



? Cosmarium antllopseum Breb. in Menegh. Synops. Desm. 1840, p. 218. 



