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. 



Yar. I. radiata. Having rays of a greenish 

 colour. 



Yar. II. curvirostris. Smaller, shorter, and flatter. 



Yar. III. latior. Broader and shorter, yellow- 

 brown. 



Yar. IY. compressa. Yery broad and flat. 



3. U. MARGARITIFEE (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 Caesar was partly attracted to 



