236 BRITISH DESMIDIACE^l. 



near the base on each side. Vertical view rather 

 narrowly elliptic, with a small 3-4-granulate tumour 

 at the middle on each side. Chloroplasts axile, with a 

 central pyrenoid. 



Zygospore unknown. 



Length 19-30/u; breadth 17-27*5 p; breadth of 

 isthmus 5 7'2 ^ ; thickness 11-16 p. 



ENGLAND.- -Leicestershire (Roy). Hants (Roy). 



SCOTLAND.- -Ross, Inverness, Aberdeen, Kincardine, 

 Forfar, Perth, Stirling, and Mull in Argyll (Roy fy 

 Bissett). Xear Lerwick, Shetlands ! 



IRELAND. Dublin and AYicklow (Archer). 



Geoc/r. Distribution.- -S. France. Germany. Silesia 

 in Austria. Norway. Sweden. Denmark. Iceland. 

 Greenland. E. Africa. Azores. United States. Brazil 

 (var.). Paraguay. Patagonia. 



This small species is closely allied to C. subcrenatum and 

 C. subcostatum, but is very mucli rarer tlian either. It does 

 not appear to have been very clearly understood in the past, 

 and most of the Desmids which have been recorded under the 

 name of C. calcareum should be relegated elsewhere. 



Both the granulation and the central protuberance are 

 subject to slight variation, and it is sometimes well nigh 

 impossible to distinguish between C. calcareum and the 

 smaller specimens of C. subcostatum forma minor. The only 

 constant distinction is the presence in the latter of at least 

 two emarginate crenations on the upper part of each lateral 



margin. 



204. Cosmarium subcostatum Xordst. 

 (PI. LXXXVII, figs. 8-5.) 



Cosmarium subcostatum Nordst. Desm. Ital. 1876, p. 37, t. 12, f. 13 ; De 

 Toni, Syll. Alo-. 1889, p. 1028 -, Schmidle in Ber. Deutsch. Botan. Ges. x, 

 1892, p.' 208, t. 11, f. 10-12 ; West, Alg. W. Ireland, 1892, p. 157 ; Alg. 

 Engl. Lake Distr. 1892, p. 728; Borg. Ferskv. alg. Ostgronl. 1894, p. 12, 

 t. 1, f . 4 ; Eoy & Biss. Scott, Desm. 189-1, p. 175 ; Nordst. Index Desm. 

 1896, p. 244 ; West & G. S. West, Alg. S. England, 1897, p. 489 ; Alga-fl. 

 Yorks. 1900, p. 78 : Borg. Freshw. Alg. Faeroes, 1901, p. 226 ; West & 

 G. S. West, Alg. N. Ireland, 1902, p. 39 ; Scott. Freshw. Plankton, I. 

 1903, p. 527 ; G. S. West, W. Indian Freshw. Alg. 1904, p. 285 ; Larsen, 

 Freshw. Alg. E. Greenland, 1904, p. 89; West & G. S. West, Freshw. 

 Alg. Orkneys and Shetlands, 1905, p. 21 ; Further Contrib. Plankton 

 Scott. Lochs, 1905, p. 484; G. S. West, Alg. Third Tanganyika Expedit, 

 1907, p. 121. 



Ursinella subcostata Kuntze, Re vis. gen. plant. 1891, p. 925. 



