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scuts a toothed hinge. The lower face of the valve is nacrous, but 
shaded with purplish violet, copreous, and iridescent; the anterior 
face is of a green colour, which varies from tender to blackish green. 
Among the species found 
!n European seas may be 
ftoted the Rhine mussel, a 
large species, the nacre of 
'vhich is employed for or- 
namental purposes. TJnio 
** ttoralis (Cuvier), repre- 
sented in Fig. 15G, and 
fbe painter’s mussel, TJnio 
pietorum (Fig. 157), em- 
ployed in the arts to con- 
lain certain colours. Those 
known as the river mussels 
ar e leathery, of an insipid 
Fig- 156. TJnio littoralis (Cuvier). 
and scarcely eatable : 
flic finest species are found in the great American rivers. 
Mussels, as we have seen, produce pearls of moderate value. Linnaeus, 
Fig. 157. TJnio pietorum (Linnreus). 
^"ho ^y ag aware 0 f pp e or igin 0 f the Pintadine pearls, and of pearls in 
§ e neral, was also aware of the possibility of producing them artificially 
2 b 2 
