CONCHIFEKA. 



287 



not uncommon now to find pearls which are sold for one 

 or even two pounds. 



In ancient times Britain was celebrated for pearls, and 

 Suetonius says that Julius Caesar was induced to visit 

 England to obtain them ; he only obtained enough, how- 

 ever, to cover a buckler, which he afterwards dedicated to 

 Venus Genetrix, and hung up in her temple. 



Unio. Retz. — Shell thick, solid, surface smooth, fur- 

 rowed, or nodulous ; trans- 

 verse, equivalve, inequilate- 

 ral ; bosses prominent and 

 eroded ; teeth grooved, solid, 

 short, and oblique ; ligament 

 external; the posterior mus- 

 cular impression is always 

 compound ; pallial simple. 

 Animal, shaped like the shell, thick, mantle freely open, 

 anteriorly with simple edges; branchial region fringed 

 with numerous cirrhi, anal, tube-like, plain; foot large, 

 broad, and compressed; labial palpi ovate.* — 200 species; 

 also a few fossil. 



The Unio is found in the rivers of Europe, both the 

 Indies, and elsewhere, particularly in North America, where 

 they seem to swarm. Three species are British. The 

 animals are eaten in Europe, often roasted in the shell. 

 They are called the fresh-water mussel : they bury them- 

 selves in the sand or mud, with the bosses undermost, and 

 sometimes produce tolerably large pearls; the valves in 

 some species are not quite closed, and they are often 

 highly iridescent within, sometimes white, at others pink 

 or purple : the colour, however, varies. 



* Forbes's British MolL 



