186 BRITISH DKSMIDIEiE. 



Micrasterias tricyclia, Ehr. hifusor. t. 11. f. 8. a, 6 (1838). 

 Pediastrum pertusum, Kiitzing, Phycologia Germanica, p. 143 (1845). 

 Pediastrum triajclium, Hassall, Brit. Freshwater Algce, t. 92. f. 1 (1845). 



Aberdeen, Mr. P. Grant. Storrington, Sussex, Mr. Jenner. 

 Germany, Ehrenberg. 



Frond consisting of from one to three circles of cells arranged round one or 

 two central ones. The number of cells, as in Pediastrum Selencea and P. 

 Boryanum, generally consists of 5 in the first circle, 1 in the second, and 1 5 

 in the third ; but I have seen fronds with four cells forming a circle about 

 two central ones. Ehrenberg' s figures represent all the cells as alike in 

 form, and this was the case in specimens sent me by Mr. P. Grant ; but 

 Mr. Jenner finds the inner cells quadrate, and only the marginal ones notched. 

 In all the varieties, however, the inner cells are so placed as to leave hyaline 

 spaces which have the appearance of perforations. The marginal cells have, 

 on their free side, a wide triangular notch, about equal to the fourth part of 

 a square ; were this filled it would make the cell quadrate, consequently the 

 sides and base of the cell form rectangular triangles, and the terminal lobes 

 taper to an acute point. 



Length of cell in outer circle ^ ^'gg of an inch ; breadth -g-^g-g-. 



Tab. XXXI. fig. 6. a, b. fronds with endochrome. 



7. P. granulatum (Kiitz.) ; cells granulated ; lobes of marginal cells 

 tapering. 



Pediastrum granulatum, Kiitzing, Phycologia Germanica, p. 143 (1845); in 

 lit. cum icone. 



"Weston Bogs near Southampton, Mr. Jenner. 



Germany, Kiitzi^ig. 



Frond composed of six cells circularly arranged around two subquadrate 

 central ones ; the marginal cells have lobes gradually tapering into short points, 

 and all are rough with minute granules. 



I have seen no specimens of this species, but Mr. Jenner' s drawings exactly 

 agree with one sent me by Professor Kiitzing. 



Length of cell in outer circle -a-oVo ^^ ^^ ^^^^^ 5 breadth xiVr- 



Tab. XXXI. fig. 8. a. frond with endochrome ; b. empty frond. 



8. P. Najjoleonis (Turpin) ; six angular cells forming a circle round 

 two central ones ; lobes of marginal cells cuspidate ; notch wide. 



Helierella Napoleonis, Turpin, Bid. des Sc. Nat. par Levr. Atl. Veg. ves. 



fig. 20 (1820) ; Mem. du Mus. v. 16. t. 13. f. 21. 

 Micrasterias Napoleonis, Kiitzmg, Synop. Diatom, in Linncea 1833, p. 602. 



Ehrenberg, Infus. p. 156. t. 11. f. 3. 

 Pediastrum Napoleonis, Meneghini, Synop. Desmid. in Limicea 1840, p. 212. 

 Pediastrimi hexactis, Hassall, Brit. Freshwater AlgcB, t. 92. f. 5 (1845). 

 Pediastrum excavatum, Hassall, I. c. t. 92. f. 6 (1845). 



Ashdown Forest, Sussex, Mr. Jenner. Swansea, J. R. Near Aberdeen, 

 Mr. P. Grant. 



Germany, Kiitzing, Ehrenberg. 



