218 BRITISH DESMIDIACE^. 



After very careful consideration the writer has failed to find 

 any essential differences between 0. filiforme (Ehr.) R. & B. and 

 0. Nordstedtianum Turn. Only one difference seems to have been 

 recognised by earlier writers, namely, that 0. filiforme has 

 larger or smaller spaces between the adjacent cells of the fila- 

 ment, whilst in 0. Nordstedtianum adjacent cells are contiguous 

 with one another. As Liitkemuller ('Zellm. Desm.' 1902, p. 367) 

 has shown, however, the cells are actually separated by gela- 

 tinous cushions, and it is presumably the size of these which 

 determines the spacing of the cells. It is improbable that specific 

 distinctions can be based on such a character, and it has therefore 

 been deemed better to unite the two under the older name of 

 0. filiforme (Ehr.) R. & B. 



2. Onychonema laeve Norclst. 

 (PI. CLX, figs. 15, 16.) 



Onychonema Iceve Nordst. Desm. Brasil, 1870, p. 206, t. 3, f. 34 ; Reinsch, 

 Contrib. Fung, et Alg. 1875, p. 93, t, 15, f . 4 ; De Tom, Syll. Alg. 1889, 

 p. 796 ; Turn. Freshw. Alg. E. India, 1893, p. 139, t. 17, f. 15A ; Roy & 

 Biss. Scott. Desm. 1893, p. 11 ; Racib. Desm. Tapakoomas, 1895, p. 32 ; 

 West & G. 8. West, Alg. Ceylon, 1902, p. 193 ; Alg. Burma, 1907, p. 224, 

 t, 12, f. 8-10. 



Xanthidiastnan paradoxum Delp. Spec. Desm. Subalp. 1877, p. 80, t. 3, 

 f. 27-33. 



Cells larg'er than in 0. filiforme, slightly broader than 

 long, deeply constricted, sinus narrow for part of its 

 length, dilated at the apex, and opening widely ; semi- 

 cells oblong or subreniform, attenuated towards the 

 lateral angles and ending in a long stout converging 

 spine ; apical processes rather shorter than the spines ; 

 vertical view elliptic, drawn out into a spine at the two 

 poles. Filaments usually embedded in a mucous in- 

 vestment. 



Zygospores spherical, with many short, stout, simple 

 spines. 



Length 16-1 7 pt. ; breadth, without spines, 20 "5-25^ ; 

 including spines, 25-46 \i : breadth of isthmus 6 \L ; 

 diam. zygosp., without spines, 17-20 pi; with spines, 

 24-26 pJ 



SCOTLAND.- -Found once by the side of the old road 

 from Aboyne to Kincardine O'Neil, about a mile from 

 Aboyne, Aberdeen (Roy & Biss.). 



