224 BRITISH DESMIDIACE^. 



Cells very small, as long as or slightly longer than 

 broad, constriction moderately deep, sinus obtuse and 

 open ; semicells elliptical, with truncate apices ; lateral 

 margins provided with 3 very minute granules ; semi- 

 cells in side view subcircular. Cells united to form 

 twisted filaments, destitute of a gelatinous sheath. 



Zygospore unknown. 



Length 8-9 '5 pi ; breadth 8 '5-9 '5 pi ; thickness 5 \JL : 

 breadth of isthmus 4-5 '5 (JL. 



ENGLAND; Skipwith Common, E. Yorks ! Har- 

 borne, and in the plankton of Bracebridge Pool, Button 

 Park, Warwickshire ! 



WALES. Capel Curig, Dolbadarn Castle, near Llan- 

 beris, and Llyn-y-cwm-ffynon, Carnarvonshire ! 



SCOTLAND.- -Rhiconich, Sutherland ! 



IRELAND. --Near Glenties, Donegal ! 



Geogr. Distribution. Germany. Australia. Madagas- 

 car. Central and E. Africa. United States. 



This species, which is nearest to Sp. tetragomrm W. & G. S. 

 West, is one of the least rare of the British species of Spon- 

 dylosium, although, being, at the same time, not at all common. 



Some confusion has arisen owing to the fact that it was not 

 made clear in the older compilations of Rabenhorst and De Toni, 

 whether the protuberances of Sp. depressum Breb. are apical 

 or lateral in position. In true Sp. depressum Breb. they are, of 

 course, apical. This species has never been found in Britain. 

 The looseness of these descriptions led to a form identical with 

 Sp. papillosum West being figured by Kirchner (' Micr. Pflanz. 

 Siissw.' 1891, p. 21, t. 2, f. 61) as Sp. depressum. Thus Sp. papil- 

 losum W. & G. S. West embraces Sp. depressum Kirchn., but not 

 Breb. 



5. Spondylosium Lundellii Borge. 



Spondylosium pulchrum forma Lund. Desm. Suec. 1871, p. 93, t. 5, f. 17 ; 



Delp. Spec. Desm. subalp. 1877, p. 77, t. 3, f. 11. 

 Sp. Lundellii Borge, Sao Paulo Alg. 1919 p. 71, t, 6, f. G. 



Cells of medium size, about 1| times broader than long, 

 constriction not deep, sinus acute, opening widely ; semi- 



