196 r.KiTiSH DESMIDEACEJ;. 



C. Ungerianum has been recorded by Bennett from Hind- 

 head, Surrey (vide Bennett, ' Fresliw. Alg. S.AV. Surrey/ 

 1892, p. 10, t. 2, f. 12-18), but his figures appear to be merely 

 caricatures of C. margaritiferum. \Ve have ourselves never 

 seen any Cosmarium strictly comparable with C. Ungerianum, 

 but from the South of England we have collected a most 

 interesting variety of it. 



Yar. subtriplicatum West & Gr. S. "West. (PI. XCI, 



fig. 7.) 



C. Ungerianum (Xiig.) De Bary var. subtriplicatum West & G. S. West, 

 Alg. S. England, 1897, p. 490. 



A variety with oblong-rectangular semicells, supe- 

 rior angles rounded. 



Length 67 ^ ; breadth 54 p.; breadth of isthmus 

 22jit; thickness 36 /x. 



ENGLAND.- -Near Chapel "Wood, S."W. Surrey! 



This variety occurred in fair abundance attached to the 

 submerged stems of Scirpus lacustris in a large mill-pond. 

 In its granulation it stands alone among British Desmids. 

 It is of the same dimensions as the typical form, and has the 

 same arrangement of granules, but the outward form of the 

 semicells is very different. At first we considered it might 

 be a large variety of C. triplicatum Wolle (consult W. & Gr. S. 

 West, ' Some Desm. U. S/ 1898, p. 309 and text-fig. 5), but 

 careful comparison with specimens of that species shows that 

 although the external form is the same, yet the English plant 

 is of larger size, and the arrangement of the granules is very 

 like that in C. Ungerianum. 



183. Cosmarium prsemorsum Breb. 

 (PL LXXXIV, figs. 1-5.) 



Cosmarium prsemorsum Breb. Liste Desm. 1856, p. 128, t. 1, f. 8 [figure 

 poor] ; Arch, in Pritch. Infus. 1861, p. 733 ; Eabeiih. Flor. Europ. Alg. 

 Ill, 1868, p. 160 ; Nordst. Norges Desm. 1873, p. 12, t. 1, f . 1 ; Cooke, 

 Brit, Desm. 1887, p. 107, t. 42, f . 2 ; De Toni, Syll. Alg. 1889, p. 1000 ; 

 West, Alg. N. Wales, 1890, p. 289 ; Alg. W. Ireland, 1892, p. 155 ; Ala:. 

 Engl. Lake Distr. 1892, p. 728; Schmidle, Beitr. Algenfl. Schwarzwald, 

 u. Kheineb. 1893, p. 101 ; Eoy & Biss. Scott. Desm. 1894, p. 171 ; 

 Schmidle, Beitr. alp. Alg. 1895, p. 454, t. 15, f. 22-25 (forms) ; Nordst. 

 Index Desm. 1896, p. 205 ; West & G. S. West, Alg. S. England, 1897,. 

 p. 490 ; G. S. West, Alga-fl. Cambr. 1899, p. 218 ; West & G. S. West, 

 Alga-fl. Yorks. 1900, p. 75 ; Bore;. Fresliw. Alg. Faroes, 1901, p. 225 ; 

 West & G. S. West, Alg. X. Ireland, 1902, p. 39; G. S. West, Treatise 

 Brit. Freshw. Alg. 1904, p. 167, f. 62 H ; West & G. S. West, Fresliw, 



