133 



29- Cosmarium pygmaeum Arch. 

 Archer in Quarterly Jour. Micr. Sci. 1864. 

 The typical form of this minute Desmid was scarce. 

 Size : long. 9,5 [x, lat. io |j., lat. isthm. 2,5 [x. 



30. Cosmarium pyramidatum Breb. 

 De Brébisson in Ralfs : Brit. Desm. 

 General in one collection. 



31. Cosmarium subcrenatum Hantzsch. 

 Hantzsch in Rabenhorst : Algen. 



This widely-distributed species was quite general. 



32. Cosmarium subtumidum Nordst. 



NORDSTEDT in WiTTR. & NoRDST ! ExsÌCC. n. 178. 



Abundant. 



33. Cosmarium venusium (Bréb.) Arch. 



De Brébisson : Liste Desm., Archer in Pritch. Infus. 

 This distinct species occurred abundantly. 



Genus Xanthidium Ehrenberg 1837. 



34. Xanthidium armatum (Bréb.) Rabh. 



De Brébisson in Meneghini : Synopsis Desm., Rabenhorst : 

 Deutschl. Kryptogamenflora IL 



Generally represented in some collections. 



Genus Arthrodesmus Ehrenberg 1837. 



35. Arthrodesmus octocornis Ehrbg. 

 Ehrenberg : Infus. 



Scarce in a single sample. 



36. Arthrodesmus trispinatus W. West. 

 W. & G. West : Algae North Ireland 1903. 



This very extraordinary Alga was observed in one collection. 

 None of the specimens contained chloroplast, so the eventual 

 removal of the species to Tetraedron is stili uncertain. 



