COSMAKIOL 155 



tuberance at the middle on each side, slightly constricted 

 below the poles, which are inflated and granulate. 



Zygospore globose, furnished with long, often 

 slightly curved spines, arising from broad, conical 

 bases, and furcate-emarginate at the apex. 



Length 27-oo /u ; breadth 38-45 /LI ; breadth of 

 isthmus 9*6-12^; thickness 18-25 /u; cliam. zygosp. 

 without spines 35-42*5 /*, with spines 75-83 /LI. 



ENGLAND.- -Rawcliffe Common, AY. Yorks ! Strensall 

 Common, X. Yorks ! Xear Bristol, Gloucestershire 

 (Thwaites). Harefield, Middlesex! Piltdown Common, 

 Sussex (Jenner). Cornwall (with zygospores) ! 



SCOTLAND. --Aberdeen, Kincardine, Forfar (Roy 

 Busett). 



(jreocjr. Distribution- -France. Germany. Sweden. 

 India. United States. Brazil. 



C. commissurale is a characteristic species, and is very rare 

 except in Cornwall, in tlie western districts of which county 

 it is generally distributed, often occurring in abundance in 

 small pools and ditches. 



Var. acutum Breb. 



C. commissurale Breb. var. acutum Breb. Liste Desm. 1856, p. 131 ; Koy 

 & Biss. Scott. Desm. 1893, p. 44. 



Lateral angles (or lobes) of semicells narrower and 

 attenuated. 



Length and breadth as in the typical form. 



SCOTLAND.- -Xear Bishop's Loch and near Aboyne, 

 Aberdeen ; Mavis Bank, Loch of Lumgair, near Stone- 

 haven, and Dalbrake in Strachan, Kincardine (Rot/ 

 $ Bisseti). 



Geoyr. Distribution.- -France. 



Var. crassum Xordst. (PI. LXXVIII, figs. 15, 16.) 



C. commissurale Breb. var. crasswn Nordst. Desm. Brasil. 1870, p. 213, 

 t. 3, f. 19; West, Alo-. W. Ireland, 1892, p. 158; Borge, Alg. erst. 

 Eegnell. Exped. II. Desmid. 1903, p. 100. 



Cells about 1J times as broad as long, sinus not 

 closed but not nearly so much widened inwardly as in 



