BUITISH DESMIDIEJS. 187 



I greatly doubt whether this species is distinct from Pediastrum Boryanum. 

 Its claim to rank as a species depends on the number and arrangement of its 

 cells. The cells themselves are variable in form. The notch of the marginal 

 ones is rounded, and usually voider than in the allied species. 



Length of cell in outer circle from y-jVg to Y4V3 of an mch ; breadth from 

 _J to 1 



1813" 1088' 



Tab. XXXI. fig. 7. a, b, c. fronds with endochrome ; d, e. empty fronds. 



9. P. angulosum (Ehr.) ; marginal cells with angular lobes which are 

 not extended into rays ; interstices hyaline. 



Micrasterias angulosa, Ehrenberg, Abh. der Berlin Ak. p. 301 (1833) ; 



Infusor. p. 156. t. 11. f. 6. a. 

 Pediastrum angulosum, Meneghini, Synopsis Desmid. inLinncea 1840, p. 211. 



Hassall, Bi'itish Freshwater Algce, p. 391. 

 Pediastrum Boryanum, Ralfs, Annals of Nat. Hist. v. 14. t, 12. f. 7 (upper 



figure) (1844) ; Trans, of Bot. Soc. of Edinburgh, v. 2. t. 17. 



Dolgelley, /. R. Ambleside, Mr. Sidebotham. Aberdeen, Mr. P. Grant. 

 Beckley Furnace near Battle, Sussex, Mr. Jenner. 



Germany, Ehrenberg. 



Frond minute, consistmg of one or more circles of cells, with a single cell 

 in the centre ; the number of cells are generally five in the inner circle, ten in 

 the second, and fifteen in the third ; the inner cells are angular, and similar to 

 those of Pediastrum Boryanum and P. vagutn. The marginal cells are less 

 deeply notched than in those species, and the lobes are merely angular, not in 

 the least extended into processes or rays. The angle is produced by the sloping 

 of the outer margin, which frequently might be termed obliquely truncate, or 

 almost emargmate. 



Length of cell in outer circle -2^32" of an inch ; breadth -j-^j-a- 

 Tab. XXXI. fig. 11. a. frond with endochrome; b, empty frond. 



10. P. Boryanum (Turpin) ; cells arranged in one or more circles 

 round one or two central ones ; marginal cells gradually tapering 

 into two long subulate points ; notch narrow. 



Helierella Boryana, Turpin, Diet, des Sc. Nat. par Levr. Atl. Veg. ves. f. 22 



(1820) ; Mem. du Mus. v. 16. t. 13. f. 22. 

 Micrasterias Boryi, Kiitzing, Synop. Diatom, in Linncea 1833, p. 603. 

 Micrasterias Boi'yana, Ehrenberg, Abh. der Berlin Ak. p. 300 (1833) ; 



Infus. p. 157. t. 11. f. 5. a, c, g, h. 

 Pediastrum Boryanum, Meneghini, Synop. Desmid. in Linncea 1840, p. 210. 



Ralfs, Annals of Nat. Hist. v. 14. p. 470. t. 12. f. 7 (lower figure) ; 



Trans, of Bot. Soc. of Edinburgh, v. 2. p. 158. t. 17. Kiitzing, Phyc. 



Germ. p. 143. Jeimer, Fl. of Tunbridge Wells, p. 198. Hassall, Brit. 



Freshwater Algce, p. 389. 



Dolgelley, Barmouth, and Penzance, J. R. Cheshunt, Mr. Hassall. 

 Beckley Furnace near Battle, Storrington, Tunbridge Wells, &c., Sussex ; 

 Dorking, Surrey ; and near Southampton, Mr. Jenner. Manchester, Mr. Gray 

 and Mr. JVilliatnson. 



