to BRITISH DESMIDIACEJS. 



the middle on each side. Cell-wall smooth. Chloro- 

 plasts axile with one small central pyrenoid. 



Zygospore unknown. 



Length 12-13'5/i; breadth 10-14'5/x,; breadth of 

 isthmus 2 "5-4 ft ; thickness (including papilla) 1 2-13 ft. 



SCOTLAND.- -Spittal of Glen Shee, Perth! 



Geofjr. Distribution.- -Germany (form). Silesia in 

 Austria. Norway. Sweden. Bengal. Ceylon. Mada- 

 gascar (var.). Abyssinia. New Zealand (form). 

 Australia. Porto Rico. Brazil. 



C. bireme is closely related to C. polygonum, hut is distin- 

 guished by its smaller size, the different form of its semicells, 

 and the replacement of the broad central tumours by elongated 

 papillae. It is mostly a tropical species, and one of its varieties 

 (var. barbadense G-. S. West, 'West Indian Fresliw. Alg./ 1904, 

 p. 286, t. 464, f. 17) is amongst the smallest of known 

 Desmids (length 7'3-7'7 ju ; breadth 7'4-Sj). 



99. Cosmarium adoxum West & G. S. West. 



(PL LXXI, fig. 38.) 



Cosmarium adoxum West & Gr. S. West, Alg. S. England, 1897, p. 478, 

 t. 7, f. 24. 



Cells minute, suboctagonal, a little longer than 

 broad, deeply constricted, sinus very narrow and 

 slightly dilated at the apex ; semicells truncate-pyra- 

 midate with obliquely truncate basal angles, lower part 

 of sides slightly divergent, upper part of sides con- 

 vergent and very slightly retuse (almost straight), apex 

 broadly truncate and straight. Side view of semicell 

 subcircular, with a median acute papilla on each side. 

 Vertical view elliptic, with a subacute papilla at the 

 middle on each side, ratio of axes (without papilla) 

 1 :1'7. Cell-wall smooth. Chloroplasts axile, with a 

 small central pyrenoid. 



Zygospore unknown. 



Length 10-11 /x; breadth 9'5/x; breadth of isthmus 

 3 ju, ; thickness (without papilla) 5'3 //,. 



ENGLAND.- -New Forest, Hants! 



