UNIO. 19 
This shell is found in similar localities to U. tumidus, 
and often approaches it in appearance—so much so 
that there has been great doubt of its being a distinct 
species. Mr. Rogers informs me that specimens found 
in canals near Manchester are lined with a beautiful 
salmon-coloured nacre, due perhaps to the refuse at 
the bottom of the canal. 
Var. I. radiata. Having rays of a greenish 
colour. 
Var. I]. curvirostris. Smaller, shorter, and flatter. 
Var. III. latior. Broader and shorter, yellow- 
brown. 
Var. LV. compressa. Very broad and flat. 
3. U. MARGARITIFER (pearl-bearing). 
Oblong, very solid, dull black; beaks always eroded, lower 
margin incurved; very compressed. The inside is pearl 
white, sometimes pinkish. Occasionally pearls are found 
inside—white, green, or brown. Length two inches, breadth 
five inches. 
This interesting species is to be found in rivers in 
mountain districts in several parts of Great Britain, 
and also in Ireland and Man. The pearls for which 
this shell was once eagerly gathered in the Tay, the 
Irt, and the Conway, are small and worthless com- 
pared with those from the East. 
Suetonius says that Cesar was partly attracted to 
