12 BRITISH DESMIDIACE.E. 



fig". 1 c of the side view being particularly erroneous. Bali's 

 did not grasp the disposition of the protuberances on E. pin- 

 nut urn, causing Lundell ('Desm. Suec/ 1871, p. 19) to mention 

 the typical form as a " forma." The upper half of the semi- 

 cell (in fact, all that part of it above the inferior iiiterlobular 

 incisions) is quite destitute of any trace of protuberances 011 

 its surface. There is one large protuberance within each 

 lower lateral lobe, and there are three others (not four as 

 figured by Ralfs) in the centre of the basal part of the semi- 

 cell. These three are smaller and disposed in the form of a 

 triangle with one angle immediately above the isthmus. 

 Luii dell was thus quite right in his interpretation of the 

 protuberances on his Swedish specimens. 



The principal variation met with is in the upper lateral 

 lobes. These lobes are always widely emarginate when seen 

 in either the side or vertical views, but generally inamillate 

 and entire when seen in front view. In some specimens, 

 however, these lobes are very broad in front view (vide PI. 

 XXIV, fig. 6), and they may be rounded-quadrate with ret use 

 margins. Every state is met with between the ordinary 

 mamillate condition and the retuse condition, and the two 

 extremes mav be found on the same cell. These forms 



t/ 



with the broad, retuse, upper lateral lobes greatly resemble 

 E. oblongum, but can be at once distinguished in either the 

 side or vertical view. 



5. Euastrum oblongum (Grev.) Ralfs. 

 (PL XXXIV, figs. 7-9 ; PL XXXV, fig. 2.) 



? ? Euastrum Pecten Ehrenb. Entwick. Lebends. d. Infus. 1832, p. 82 



(Description insufficient for identification). 

 Echinella oblonga Grev. in Hook. Brit. Flor. 1833, II, p. 398. 

 Cosmarium sinuosum Corda, Alnianach de Carlsbad, 1835, p. 121, t. 2, f. 21. 

 Micrasterias sinuata Breb. et God. Alg. Falaise, 1835, p. 55, t. 7. 

 Heterocarpella sinuata Breb. in Cheval. microscop. et usage, Paris, 1839, 



p. 272. 



Cosmarium oblongum Breb. in Menegh. Synops. Desm. 18-40, p. 221. 

 Eutomia oblonga Harv. Man. Brit. Alg. 1841, p. 188. 

 Euastrum oblongum (Grev.) Ralfs in Ann. Mag. Nat. Hist, xiv, 1844, p. 



189, t. 6, f. 4 ;' Hass. Brit. Freshw. Alg. 1845, p. 380, t. 91, f. 1 ; Ralfs, 



Brit. Desm. 1848, p. 80, t. 12 ; Arch, in Pritch. Infus. 1861, p. 728, t. 3, 



f. 11 ; Rabenh. Flor. Europ. Algar. Ill, 1868, p. 181 ; Delp. Desm. 



subalp. 1873, p. 99, t. 6, f. 26-30 ; Kirchn. Alg. Schles. 1878, p. 157; 



Wolle, Desm. U.S. 1884, p. 98, t. 25, f . 5 (figure bad) ; Cooke, Brit. 



Desm. 1886, p. 64, t. 31, f . 2 ; Hansg. Prodr. Algenfl. Bohni. 1888, p. 



204 ; De Toni, Syll. Alsr. 1889, p. 1086 ; West, Alg. W. Ireland, 1892, p. 



136; Alg. Eng. Lake District, 1892, p. 722 ; Roy & Biss. Scott, Desm. 



1893, p. 177 ; Nordst. Index Desm. 1896, p. 185 ; West & G. S. West, 



Alg. S. England, 1897, p. 483 ; Alcra-fl. Yorks. 1900, p. 61 ; Alg. N. 



Ireland, 1902, p. 27 ; Scott. Freshw. Plankton, I, 1903, p. 525. 



