PLATE CI. 



FIGS. PAGE 



1-8. Cosmarium bi return Breb. 1 and 2, x 400 (after 

 Bali's) ; 3-8, x 20, various forms from Welsh 

 Harp, Middlesex . . .25 



9. C. biretum forma triquetra Breb. x 330 (after 



Brebisson). Outline of basal view of semicell 28 

 10-15. C. biretum var. trigibberum Nordst. 10, x 400 

 (after Nordstedt) ; 11, x 400 (after Nordstedt) ; 

 12-15, various forms, x 520; fig. 11 represents 

 the form described by Nordstedt as " forma 

 supernumeraries ' . . .28 



