186 BRITISH DESMIDIEjE. 



Micrasterias tricyclia, Ehr. Infusor. t. 11. f. 8. a, h (1838). 

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

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



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

 Germany, Ehrenbery. 



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

 two central ones. Tlie 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 margmal 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 thfe 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-^^. 



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



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

 tapering. 



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

 lit. cum icone. 



Weston Bogs near Southampton, Mr. Jenner. 



Germany, Kiitzing. 



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 -g-oVo ^^ ^"^ i\\(^ ; breadth ygVy 



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



8. P. Napoleonis (Turpin) ; six angular cells fonning a circle round 

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



Helierella Napoleonis, Turpin, Diet, des Sc. Nat. par Levr. Atl. Feg. ves. 



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

 Micrasterias Napoleonis, Kiitzing, Synoj). Diatom, in Linncea 1833, p. 602. 



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

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

 Pediastrum hexaetis, Hassall, Brit. Freshwater Alyce, t. 92. f. 5 (1845). 

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



Ashdown Forest, Sussex, Mr. Jenner. Swansea, J. 11. Near Aberdeen, 

 Mr. P. Grant. 



Germany, Kiitzing, Ehrenberg. 



