188 BRITISH DESMID1E-(E. 



Germany, KUtzing, 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. 



Pediastrum 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 ia outer circle from -gVo" ^° rsVa ^^ ^"^ mch ; breadth from 



I to 1 



2 7 3 2 " 2 2 2 2* 



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



1 1 . 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) ; Infiis. 



p. 158. t. 11. f. 9. 

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



p. 293. t. 1. f. 21 (1841). 

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



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

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



cum icone. 

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

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



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

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

 Surrey ; and near Southampton, Mr. Jenner. 



Germany, Ehrenberg, Kutzing. Maine to Virgmia, 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 m 

 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 mmute 

 teeth at the end. 



Length of cell ui outer circle from yttj ^^ ¥W ^^ ^^^ ^i^*^^ ' breadth from 

 _-J to —J 



1515 ""^ 1020* 



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



