G6 BRITISH DESMIDIACE.E. 



Cells proportionately narrower ; semicells slightly 

 attenuated from base to apex ; constriction very deep, 

 isthmus very narrow. Side and vertical views more 

 compressed. 



Length IS JJL ; breadth 7 '7 ^\ breadth of isthmus 

 1'5 //, ; thickness 4 - 8 p.. 



ENGLAND.- -Strensall Common, ]$T. Yorks ! 



86. Cosmarium minimum AVest & Gr. S. West. 

 (PI. LXXI, figs. 1, 2.) 



Cosmarium minimum West & Gr. S. West, Alg. Madag. 1895, p. 58, t. 8, 

 f. 10; Nordst. Index Desm. 1896, p. 171; West & GK S. West, Welw. 

 Afric. Freshw. Alg. 1897, p. 118; Alga-fl. Yorks. 1900, p. 91; Freshw. 

 Alg. Ceylon, 1902, p. 166. 



Cells minute, a little longer than broad, fairly deeply 

 constricted, sinus sublinear and slightly open ; semicells 

 transversely rectangular, angles scarcely rounded, sides 

 and apex almost straight. Side view of semicell sub- 

 circular. Vertical view elliptic, ratio of axes about 

 1 : T7. Cell-wall smooth. Chloroplasts axile with a 

 small central pyrenoid. 



Zygospore unknown. 



Length S'4-10'5 p ; breadth 7*2-9 p. ; breadth of 

 isthmus 3-5 p.; thickness -A'o-o'o p.. 



ENGLAND.- -Pilmoor, X. Yorks ! 



Geogr. Distribution. Ceylon. Madagascar. TT. Africa. 



This minute species is characterized by its rectangular 

 semicells. It Las principally a tropical distribution. 



87. Cosmarium pusillum (Breb.) Arch. 

 (PI. LXXI, figs. 3, 4.) 



Euastrum pusillum Breb. Liste Desm. 1856, p. 125, t. 1, f. 7. 



Cosmarium pusillum (Breb.) Arch, in Pritch. Infus. 1861, p. 731 ; Rabenh. 



Flor. Europ. Alg. Ill, 1868, p. 169 ; Kirchn. Alg. Schles. 1878, p. 153 ; 



Haiisg-. Prodr. Alarenfl. Bohm. 1888, p. 201 ; Boldt, Desm. Gronland, 



1888, p. 17; De Toni, Syll. Alg. 1889, p. 1045; Eoy & Biss. Scott. 



Desm. 1894, p. 172 ; Nordst. Index Desm. 1896, p. 214 ; West & G. S. 



West, Alg. N. Ireland, 1902, p. 34 ; Freshw. Alg. Ceylon, 1902, p. 166. 

 Ursinella pusilla Kitntze, Revis. gen. plant. 1891, p. 925. 

 Cosmai-ium pusillum var. retusum Turn, forma Turn. Freshw. Alg. E. 



India, 1893, p. 71, t. 10, f. 26. 



