188 BRITISH DESMIDIE^. 



Germany, Kiitzing, Ehrenberg. Falaise, Brebisson. Maine to Mexico, 

 Bailey. 



Cells generally arranged in one to three circles round a central cell. The 

 number of cells consists of five in the first circle, ten in the second, and fifteen 

 in the third ; but these numbers are not invariable ; sometimes there are two 

 central cells, and still more frequently the numbers in the circles differ from 

 those just stated. The inner cells are five- or six-angled, broader than long, 

 with a slight concavity on the outer margin ; the marginal cells are biradiate, 

 the rays subulate, the notch narrow. 



Pecliastrum Boryanum differs from P. vagum in the gradually tapering acute 

 lobes of the outer cells ; from P. angulosum it may be known by the lobes, 

 which are elongated into rays, and not merely angular, as in that species. 



Length of cell in outer circle from -g-oVa ^o ^^^33 of an inch ; breadth from 



1 fn 1 



27 32 ^^ 2 2 2 2* 



Tab. XXXI. fig. 9. a. frond with endochrome; b. empty frond. 



11. P. ellipticum (Ehr.) ; cells variable in number and arrangement; 

 lobes of marginal ones suddenly contracted into short, cylindrical, 

 obtuse processes. 



|3. processes of the lobes truncato-emarginate. 



Micrasterias elliptica, Ehrenberg, Abh. der Berlin Ak. p. 302 (1833) ; Infus. 



p. 158. 1. 11. f. 9. 

 Micrasterias, No. 3, Bailey, American Journal of Science and Arts, v. 41. 



p. 293. t. l.f. 21 (1841). 

 Pediastriim Boryanum, Ralfs, Annals of Nat. Hist, v. 14. t. 12. f. 8 (1844) ; 



Trans, of Bot. Soc. of Edinburgh, v. 2. t. 17. 

 Pediastrum vagum, Kiitzing, Phycologia Germanica, p. 143 (184.5) ; m lit. 



cum icone. 

 Pediastrum constrictum, Hassall, Brit. Freshioater Algce, p. 391 (1845). 

 Pediastrum ellipticum, Hassall, Brit. Freshwater Algce, t. 92. f. 2 (1845). 



Dolgelley, /. R. Aberdeenshire and Banffshire, Mr. P. Grant. Near 

 Bristol, Mr. Thwaites. Beckley Furnace near Battle, Sussex ; Dorkmg, 

 Surrey ; and near Southampton, %Ir. Jenner. 



Germany, Ehrenberg, Kiitzing. Maine to Virginia, Bailey. 



Frond larger than that of any other species, often very irregular in form ; 

 cells numerous, but varying much in number ; the arrangement of the inner 

 ones, especially in the larger specimens, is more or less irregular, and not in 

 distinct circles, like those in the preceding species. The notch of the mar- 

 ginal cells is narrow, the lobes terminated by a cylindrical process, which 

 appears to me rounded at its apex ; but Mr. Jenner usually finds two minute 

 teeth at the end. 



Length of cell in outer circle from yy 5^ to -^\-^ of an inch ; breadth from 

 _ J to I 



1515 ^^ 1020* 



Tab. XXXI. fig. 10. a, b, c. fronds with endochrome ; d. empty frond. 



