UNIO. 149 
Var. I. vradidta (Mog.). Having greenish-coloured 
rays. 
Var. II. curvirdstris (Vorm.). Smaller, shorter, flatter. 
Var Wien vavor. (fe7_). Broader, ‘shorter, yellow- 
brown. 
Var. 1V. compréssa (Jeff.). Very broad and flat. 
Sub-genis.—MARGARITANA Schum. 
3. U. MARGARI{TIFER (fearl bearing) Linné. Pl. IX., f. 12. 
Oblong, compressed, very solid, dull black; deaks always eroded, 
lower margin nearly straight. The inside is pearl-white, sometimes 
pinkish. Occasionally pearls are found inside—white, green or brown. 
i2un.  B. 5.n: 
This interesting species known as the ‘pearl mussel’ is 
to be found in rivers in mountain districts in several parts 
of Great Britain from Shetland to Cornwall, but only to 
the west of a line drawn from Scarborough to Exeter ; and 
also in Ireland and the I. of Man. The pearls for which 
this shell was once eagerly gathered in the Tay, the Irt 
and the Conway, are small and worthless compared with 
those from the East. 
Suetonius says that Ceesar was partly attracted to Britain 
by the reports of pearls found there, and Pliny states that 
he covered a buckler with them, which he dedicated to 
Venus Genetrix. 
Forbes and Hanley think that ‘“ Czesar’s buckler was 
more probably covered with the pearls from JZytzlus 
