Plate Y< 
20. Cosmarium margaritiferum. 
21. Cosmarium margaritiferum 
(empty frond). 
22. Cosm. margaritiferum (end view). 
23. Ankistrodesmus falcatus. 
34. Figure of a Bottle attached to the 
end of a walking-stick by an 
india-rubber band. 
25. Navicula didyma. 
20. Pinnularia major. 
