SPH.EROZOSMA. 211 



ENGLAND.- -Plankton of Ennerdale Water, Cumber- 

 land !, and of Brother's Water, Westmoreland ! 

 SCOTLAND. --Near Scalloway, Shetlands ! 



The differences between this variety and Sph. Aubertianum 

 var. Archeri are often very slight, so that it is difficult to distin- 

 guish between them. The latter Desmid seems, however, to 

 be relatively longer, whilst the punct illations in SpJi. vertebratum 

 var. punctidatum are more evenly distributed. 



Var. latins W. & G. S. West, (PL CLIX, fig. 11.) 



Sjth. vertebratum var. latins West & G. S. West, Alg. S. Engl. 1897, p. 497, 

 t. 6, f. 7. 



Cells much wider than in the type, up to If times 

 broader than long ; sinus narrower and deeper ; apex 

 of semicell more convex. 



Length 15-16 [i ; breadth 25-27 [JL ; breadth of isth- 

 mus 5 '5-7 "5 JJL. 



ENGLAND. Esher West End Common, Surrey ! 



3. Sphserozosma excavatum Ralfs. 

 (PL CLX, figs. 1-3.) 



Splicerozosma excavatum Ralfs in Ann. Mag. Xat. Hist. vol. 16, 1845, p. 15, 

 t. 3, f. 8 ; Brit. Desm. 1848, p. 67, t. 6, f . 2 ; De Bary, Conj. 1858, p. 45 ; 

 Arch, in Pritch. Inf. 1861, p. 724; Rabenh. Krypt.-fl. Sachs. 1863, 

 p. 178 ; Reinsch, Alg. Frank. 1867, p. 199 ; De Not. Desm. Ital. 1867, 

 p. 29, t, 1, f. 5 ; Rabenh. Flor. Europ. Alg. 1868, p. 149 ; Xordst. Desm. 

 Brasil, 1869, p. 205; Jacobs. Desm. Danem. 1875, p. 211; Kirchn. 

 Alg. Schles. 1878, p. 133 ; Wolle, Desm. U. S. 1884, p. 29, t. 4, f. 8-12 ; 

 Cooke, Brit. Desm. 1887, p. 4, t, 2, f. 2 ; Hansg. Prodr. Alg. Bohm. 1888, 

 p. 170 ; De Toni, Syll. Alg. 1889, p. 790 ; West, Alg. X. Wales, 1890, p. 6 ; 

 Alg. Engl. Lake Distr. 1892, p. 6 ; Alg. W. Ireland, 1892, p. 115 ; Gutwin. 

 Flor. Glonow Galic. 1892, p. 15 ; Roy & Biss. Scott. Desm. 1893, p. 10 ; 

 West & G. S. West, Some X. Amer. Desm. 1896, p. 231, t. 12, f. 9 ; 

 Comere, Desm. de France, 1901, p. 198, t. 16, f. 14 ; West & G. S. W T est, 

 Alga-fl. Yorks. 1902, p. 110; Alg. X. Ireland, 1902, p. 59; G. S. West, 

 Brit. Freshw. Alg. 1904, p. 175, f. 67, D-F ; West & G. S. West, Freshw. 

 Alg. Orkneys & Shetlands, 1905, p. 28; Cushman in Rhodora, 1905, 

 p. 264 ; in Bull. Torr. Bot, Club, 1905, p. 552 ; ibid. 1907, p. 615. 



Isihmosira excavata Kiitz. Spec. Alg. 1849, p. 189. 



Cells very small, usually only slightly longer than 

 broad, but sometimes as much as twice as long as broad, 

 constriction moderately deep, sinus widely excavated, 



