XANTHIDIUM. 359 



spines, the central apertures exist ; that is, in the species re- 

 ferred by Meneghini to Cosmarium these openings are met 

 with — the only character which is even supposed to belong 

 exclusively to Xanthidium. 



" I have little doubt that there arc more British species of 

 Xanthidium than I shall here describe, and indeed believe 

 that I have more than once gathered X. Idrsutiim ; but as 

 my attention was not directed to the Desmidcca at the time, 

 I neglected to examine it with sufficient care to be able to 

 state my observations with any confidence in this paper." — 

 Ralfs. 



1. Xanthidium furcatum Ehr. 

 Plate LXXXIX. Fig. 1. 



Char. Segments reniform. Spines at first marginal, sub- 

 seqiiently scattered, dividing at their terminations into 

 three or four acute divergent points. 

 Xanthidium furcatum Ehr., Infus. p. 148. tab. x. f. xxv. ; 

 Menegh. Synops. Desmid. p. 224. Xanthidium No. 2., 

 Bailey's American Bacillaria, p. 291. pi. i. fig. 15. ; 

 Ealfs, inAunals, vol. xiv. p. 466. pi. xii. fig. 1. 

 Hah. Several j^laces in Sussex : Mr. Jenner. Dolgclly, 

 and near Carmarthen : ilfr. Ralfs. High Beech and 

 Cheshunt Common : A. H. H. Aberdeen : Dr. Dickie. 

 L-eland : Mr. Moore. 



This is the finest as well as commonest species of the genus. 

 There is no other Avith which it can be confounded. 



In the figure of this species, given by Ehrenbcrg, the een- 

 tral aperture seems to be indicated. 



2. Xanthidium fasciculatum Ehr. 

 Plate LXXXIX. Fig. 2. 



Char. Segments small, reniform. Spines in pairs, and 

 usually six pairs to each segment. 

 Xanthidium aculeatum, Abhandl. d. Akademie d. ^Visscnsch. 



