208 BRITISH DESMIDIACE^;. 



Length of cells 16-5-19^ ; breadth 18-23 a ; breadth 

 of isthmus 5-8 \JL ; diam. zygosp. without spines 19-24 a ; 

 including spines, 37*5-42 p.. 



ENGLAND.- -Plank ton of Ennerdale Water, Cumber- 

 land ! 



WALES. Capel Curig, Carnarvonshire ! 



IRELAND.- Common in the plankton of Lough Aecory- 

 more, Achill Isle, Mayo ! Derryclare Lough, Gal way ! 



Geogr. Distribution.- -Finland. Australia. LTnited 

 States. 



Var. Archeri (Gutw.) W. & G. S. West. (PI. CLIX, 



figs. 14-17.) 



Sphcerozosma vertebrate m Arch, in Q. J. M. S. 1865, v. 5, p. 170 ; ibid. I860, 



v. 6, p. 274. 

 Sph. vertebratum forma Nordst. in Wittr. et Nordst. Alg. exs. no. 967^ 



fasc. 21, p. 34, 1889. 

 Sph. Archeri Gutw. Flor. Glon. Okolic Llowa, 1891, p. 29, t, 1, f. 4 ; 



Roy & Biss. Scott. Desm. 1893, p. 10 ; Gutw. Flor. Glonow Okolic 



Tarnapola, 1894, p 77. 



? Sph.filiformis Turn. Alg. E. India, 1893, p. 142, t. 17, f. 20. 

 Sph. Aubertianum var. Archeri West & G. S. West, Some N. Amer. Desm. 



1896, p. 230; Furth. Contrib. Plankton Scott. Lochs, 1905, p. 505, 



t. 6, f. 7. 



Differs from the type only in the fact that each semi- 

 cell is provided with two horizontal series of granules. 



Zygosp ore exactly similar to that of the type. 



Length 12-17 JJL ; breadth 19-27*5 \L ; thickness about 

 ll'Spi; breadth of isthmus 5 '5-7 pi; diam. zygosp., 

 without spines, 19 ^ ; length of spines up to 17 [JL. 



ENGLAND.- -Plankton of the English Lake District ! 



WALES.- -In the plankton ! 



SCOTLAND. --Near Alford and Braemar, Aberdeen 

 (Roy <& Biss.). Plankton of Lochs Shiel and Bairness, 

 Inverness !, and of Loch Eadaghoda, Lewis, Outer 

 Hebrides ! 



Geogr. Distribution. Sweden. Poland. India. 

 Australia. 



Transitional forms between Sph. Aubertianum and its var. 

 Archeri are not at all uncommon, the two rows of granules being 

 very often incomplete. The variety is frequent in plankton. 



Liitkemuller (' Desm. Bohm.' 1910) expresses the opinion that 



