64 BRITISH DESMIDIACIwK. 



(generally six) of radiating longitudinal plates, and so far they 

 resemble those of the genus Peniu in; but in three out of the 

 four species of Netrium the free edges of the plates possess con- 

 spicuous notches which are never present in the chloroplasts 

 of Pen/ium, and the fourth species has each chloroplast trans- 

 versely segmented so tluit four are present in the cell. 



1. Netrium Digitus (Ehrenb.) Itzigs. & Rothe. 

 (PL VI, figs. 14-16.) 



i-i-i i'n> Digitus Ehrenb. Entwick. Lebens. d. Infus. 1832, p. 68; Infus. 



1838, p. 94,' t. 6, f. iii ; Menegh. Synops. Desm. 1840, p. 236 ; Hass. 



Brit, Freshw. Alg. 1845, p. 376, t. 88, f. 4 ; Focke, Phys. Stud. I, 1817, 



p. 68, t. 3, f. 22. 



Closterium lamellosum Breb. Alg. Falaise, 1835, p. 59, t. 8. 

 Penium Digitus Breb. in Ralfs' Brit. Desm. 1848, p. 150, t. 25, f. 3 ; Arch. 



in Pritch. Infus. 1861, p. 751 ; Rabenh. Flor. Eiirop. Alg. 1868, iii, 



p. 118; Delp. Desm. Subalp. 1877, p. 86, t. 15, f. 50, 51 ; Kirchn. Alg. 



Schles. 1878, p. 134; Wolle, Desm. U.S. 1884, p. 34, t. 53, f. 1; Coukc, 



Brit. Desm. 1886, p. 40, 1. 16, f. 1 ; Hauptfl. Zellmembr. u. HiillganVHr 



Desm. 1888, p. 101, t. 3, f. 62 ; West, Alg. W. Ireland, 1892, p. 127 ; 



Liitkem. Desm. Attersees, 1893, p. 544 ; Roy & Biss. Scott. Desm. 1894, 



p. 251 ; West & G. S. West, Rec. publ. Desm. 1895, p. 66 ; Alg. 8. 



England, 1897, p. 478 ; Alga-fl. Yorks. 1900, p. 44; Alg. N. Ireland, 



1902, p. 21 ; Some Desm. U.S. 1898, p. 282; Freshw. Alg. Ceylon, 1902, 



p. 134. 

 Penimn In nn:l/osum Kiitz. Spec. Alg. 1849, p. 168; Breb. Liste Desm. 1856, 



p. 146, t. 2, f. 34; Kirchn. Alg. Schles. 1878, p. 135; Wolle, Desm. U.S. 



1884, p. 34, t. 5, f. 4 ; Liitkem. Desm. Attersees, 1893, p. 545. 

 Netrium Digitus (Ehrenb.) Itzigs. it Rothe in Rabenh. Alg. 1856, 110. 508 ; 



Liitkem. Zellmembr. Desniid. 1902, p. 407. 

 Penium Digitus forma curta Anderss. Sverig. Chlor. 1890, I, p. 19, t. 1, 



f. 14. 

 Penium Digitus forma recta Turn. Freshw. Alg. E. India, 1893, p. 18, t. 1, 



f. 27. 



Penium Navigium Turn. Freshw. Alg. E. India, 1893, p. 17, t. 1, f. 9. 

 Penium Digitus var. montanum Lemm. Algenn. Riesengebirges, 1896, 



p. 120, f. '15-17. 



Cells of variable size, generally large, 3-4 times 

 longer than their diameter, not constricted, elliptic- 

 oblong, gradually attenuated from the middle towards 

 the apices which are rounded truncate; chloroplasts 

 axile with about six longitudinal plates, deeply notched 

 at the free margins ; cell- wall smooth. 



Zygospore spherical, smooth and thick-walled. 



Length 1 30-387 /u; breadth 40-82 ^ ; breadth near 

 apices 18-40 /u ; diam. zygosp, 73'(5 /u ; thickness of wall 

 of zygosp. 3'2/u. 



