COSMARIUM. 19 



Harris and Lewis, Outer Hebrides ! Orkneys ! Shet- 

 land s ! 



IRELAND. Lough Anna, Donegal ! Dublin and 

 AYicklow (Archer) . Lough Derryclare, and near Round- 

 stone, G-alway ! Foxford, Mayo ! 



(leofjr. Distribution.- ^France (f. minor). Germany. 

 Galicia in Austria (f. minor). Norway. Sweden. 

 Greenland. Ceylon. Singapore. AY. and Central 

 Africa. United States. AY. Indies. Brazil (f. min or). 



It is a doubtful question whether C. mar gar it a turn should 

 he separated from C. conspersmn as a species, or whether it 

 should be placed as a variety in close association with the 

 var. latum. Its complete separation is, however, a con- 

 venience, as it is the only British Gosmariumoi. this type with 

 well-marked punctulations between the granules. The granu- 

 lation is constant in character, but the granules exhibit con- 

 siderable variation in size in different individuals. The basal 

 portion of the semicell is generally distinctly wider than the 

 apical part, owing to the greater rounding of the apical 

 angles. The slio-ht differences in the outward form of the 



O O 



semicells, and the presence of regularly arranged punctula- 

 tions between the granules, are the only characters which 

 separate C. margaritatum from C. conspersum var. latum. 



The smaller forms of this species are known as : 

 Forma MINOR (Boldt) AY. & a. S. West, AYelw. Afric. 

 Freshw. Alg. 1897, p. 121 ; C. latum var. margaritatum forma, 

 minor Boldt, Desmid. Gronhmd, 1888, p. 26. Length 44-62 /j. 

 breadth 38-48 fi ; breadth of isthmus 12-5-13-5 /LI ; thickness 

 25-30 m. (PI. XCIX, fig. 9.) 



The largest forms we have observed occurred in abundance 

 at Chippenham Fen, Cambridgeshire, and reached a length of 

 105/i. This is slightly larger than the Desmid described as 

 " C. margaritatum var. major' by Schmiclle ('Alg. Caroliii/ 

 1901, p. 347, t. 12, f. 5), but that seems scarcely to belong to 

 C. margaritatum on account of its different proportions and 

 its smooth apices. 



Forma subrotundata nob. (PL C, fig. 1.) 



Semicells relatively wider and more rounded, almost 

 reniform in outline ; granules hollow (excavated from 

 the interior). 



Length 92 //, ; breadth 80 p. ; breadth of isthmus 31 ft. 



