100 BRITISH DESMIDIACEyE. 



West, W. Indian Freshw. Alg. 1904, p. 285 ; West & G. S. West, Fresliw. 

 Alg. Orkneys and Shetlands, 1905, p. 22 ; GK S. West, Alg. Third Tan- 

 ganyika Expedit. 1907, p. 119. 



C. Menegliinii Breb. var. simplicissimum Wille, Norges Ferskv. Alg. 1880, 

 t. 1, f. 11 a. 



Euastrum (Cosmarium) Iteve Gay, Monogr. loc. Conj. 1884, p. 59. 



Euastrum (Cosmarium) leiodermum Gay, 1. c. p. 58, t. 1, f. 16. 



Cosmarium Meneghinii Breb. var. subhexagonum Hansg. Prodr. Algenfl. 

 Bohm. 1888, p. 279. 



C. leiodermum Hansg. 1. c. 1888, p. 194, 247. 



Ursinella Isems Knntze, Revis. gen. plant. 1891, p. 925. 



U. leioderma Kuntze, 1. c. p. 925. 



Cosmarium Gerstenbergii Richter, PhycotliecaUnivers. XIII, 1895, no. 635 

 cum fig. a et b ; in Hedwigia, 1895, p. 23, fig. a c (p. 24). [Vide 

 Nordst. Index Desm. 1896, p. 153; et Sclimidle, Beitr. Algenfl. Afrik. 

 1901, p. 66.] 



Cells small, about 1-J times as long as broad, very 

 deeply constricted, sinus narrowly linear with a dilated 

 apex ; semicells semi-elliptic or semi-oblong-elliptic, 

 with the basal angles slightly rounded or much 

 rounded, apex narrowly truncate and retuse. Side 

 view of semicell ovate-elliptic. Vertical view elliptic, 

 ratio of axes about 1 : 1*5. Cell- wall delicately and 

 often somewhat sparsely punctate or punctate-scrobi- 

 culate. Chloroplasts axile, one in each semicell, with 

 a central pyrenoid. 



Zygospore angular-globose, smooth, angles slightly 

 thickened. 



Length 15-34/x; breadth ll'5-23/>c; breadth of 

 isthmus 2'8-6'7/x; thickness 9-13 ju,; diam. of zy go- 

 spore 22-25 p.. 



ENGLAND. - Westmoreland ! W. and N. Yorks ! 

 Essex! Kent! Hants (I?o//). Cornwall ! (Marquand). 



WALES.- -Radnor ! 



SCOTLAND.- -Fouley, Aberdeen (Roy $ Bissett). Glas 

 Mhoel, Perth ! Argyll ! Cumbrae ! Orkneys ! 

 Shetlands ! 



IRELAND.- -Errigal, Loughs Nacung and Sproule, 

 Donegal ! Slieve Donard, Down (at 2000 ft.) ! Dublin 

 and Wicklow (Archer). 



Geocjr. Distribution.- -France. Germany. Gralicia 

 in Austria. Hungary. Italy. Spain. Portugal. 

 Norway. Poland. N. Russia. Faeroes. Nova 

 Zembla. India, Ceylon. Burma. Siam. Australia. 



