360 DESMIDE-aJ. 



zu Berlin, 1833, p. 318. X. fasciculatum Ehr., Infus. 

 p. 147. tab. x. fig. xxiv. b. Xanthidium fasciculatum 

 Ralfs, in Annals, vol. xiv. p. 166. fig. 3. c. d. e. Cos- 

 marium aculeatum Menegh., 1. c. p. 218. Euastrum 

 No. 10., Bailey's Amer. Bacil. p. 296. pL i. fig. 10. ; 

 Jenner, in loc. cit. p. 194. 



This species is smaller than the following, the segments of 

 a different form, and the spines more numerous. 



3. XANTHIDIUM POLYGONUM Hass. 



Plate LXXXIX. Fig. 4. 



Char. Frond polygonal. Segments four-angled. Spines 

 eight to each segment, in pairs, situated at the angles. 



Xanthidium fasciculatum (Bpolygonum Ehr., Infus. p. 148. 

 t. 10. fig. 24. a. Xanthidium fasciculatum ft poly- 

 gonum Kail's in Annals, vol. xiv. p. 467. pi. xii. 

 fig. 3. a. b. 



Hob. Near Dolgelly : Mr. Ralfs. Near Tunbridge Wells : 

 Mr. Jenner. 



This doubtless ought not to be regarded as a variety, but 

 as a distinct species, differing from Xanthidium fasciculatum, 

 of which it has hitherto been regarded as a variety, in being 

 altogether a much larger plant, in the polygonal form of the 

 segments, and in the number of the spines to each segment, 

 which are eight in X. poly gonum, arranged in four pairs, while 

 in X. fasciculatum they are twelve, disposed in six pairs. 



4. XANTHIDIUM ACULEATUM Ehr. 



Plate LXXXIX Fig. 3. 



Char. Segments reniform, almost globose. Spines single, 



marginal, and scattered. 



Xanthidium aculeatum Ehr., Infus. p. 147. tab. 10. fig. 23.; 

 Menegh. 1. c. p. 224. ; Ralfs, in Annals, vol. xiv. p. 467. 

 pi. xii. fig. 2. a. b. c. d. 



