PLATE VI. 

 PJSIDIUM AMNICUM (Miiller). 



1. a-l. External aspect of a series of valves of all ages from the 



Pleistocene at Grays, Essex. Typical form. 



2. a-l. - Form verging towards " var. danubialis" from the 



same locality and formation. 



3. a-l. of " var. danubialis" from the same locality and 



formation. 



4. a-v. showing transition into the small trigonal form, from 



the same locality and formation. 



*#* The scale in millimetres under each figure, or series of figures, 

 shows the amount of magnification. 



