PLATE VII. 



PISIDIUM AMKICUM (M tiller). 



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



Pleistocene of Crayford-Erith. Typical form. 

 [1 m & p show the dendritic markings characteristic 

 of this deposit. 1 s is an example of one of the 

 fractured and repaired valves that are frequent.] 



2. a-j. still younger specimens more highly magnified, from 



the same locality and formation. 



3. a-k. very young forms of " var. danubialis," from the 



same locality and formation. 



,4. a-h. larger examples of that variety, from the same 



locality and formation. 



5. a-h. from the Pleistocene at Swanscombe, Kent. Form 



intermediate between the type and " var. danu- 

 bialis." 



6, af. from the Cromerian at West Runton, Norfolk. 



Typical form. 



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

 shows the amount of magnification. 



