266 BRITISH DESMIDIACEjE. 



SCOTLAND. --Grlen Clnnie in Braemar, and Birse, 

 Aberdeen (livy fyBissett). 



Geoc/r. Distribution.- -France. Gralicia in Austria. 

 Hungary. Norway. Sweden. Denmark. Java. Japan. 

 Bengal. Burma. Central Africa. Australia. Xew 

 Zealand. United States. 



C. retusum is a rare species of characteristic form. The 

 granulation,, which is somewhat peculiar,, is exceedingly 

 variable, and not infrequently scarcely visible. It is appa- 

 rently more abundant in tropical and subtropical regions than 

 in temperate zones. 



Messrs. Roy and Bissett have described a perfectly smooth 

 variety (var. Iseve) from Japan (consult Roy & Biss. f jap. 

 Desm/p. 195). 



In view of the great variability of the granulation of this 

 species it is doubtful whether " var. vagans" Nordst. (' Alg. 

 et Char. I/ 1880, p. 5, t. 1, f. 5) should not be included with 

 the type. 



Var. angustatum nol>. (PL XCI, fig. 3.) 



C. eductum Roy & Biss. var. angustatum West, Alg 1 . W. Ireland, 1892, 

 p. 143, t. 20, f. 20. 



Cells proportionately narrower, basal angles indis- 

 tinctly 3 -undulate ; cell- wall faintly but distinctly (and 

 somewhat distantly) punctulate, punctulations stronger 

 within the basal angles and immediately below the 

 apex. 



Length 30 /x; breadth 21 *5 /* ; breadth of isthmus 

 6'5 p. ; breadth of apex 11 12'5 /*. 



IRELAND. Ballynahinch, Gralway ! 



This variety seems to be a transitional form between 

 C. retusum (Perty) Kabenh. and a Desmid which we have 

 described as (7. insequalipellicu'm (vide West & Gr. S. West,, 

 1 Alg. Madag/ 1895, p. 54, t. 6, f. 28-29), which has a wide 

 distribution in the tropical and subtropical regions of both 

 the eastern and western hemispheres. C. retusum var. 

 angustatum has the same proportions as C. insequalipellicum, 

 but has neither the unequally thickened basal angles nor the 

 minutely undulate apex of that species. The cell-wall is also 

 differently puiictulated, the punctulations of C. insequali- 

 pellicum having a denser and a perfectly even disposition. 



