unio. 139 



open in front and anteriorly, with simple edges ; branchial 

 region fringed with numerous cirrhi, anal tube-like, plain. 

 Foot large, broad, compressed. Labial palps ovate. 



The rivers of North America swarm with species of this 

 beautiful genus, but in Europe we have very few, and in 

 Britain only three forms. A fourth, Unio littoralis, still 

 living in France and other parts of the continent, inha- 

 bited our area during the pleioceue epoch, but has long 

 since disappeared. 



Schumacher constituted his genus Margaritana for those 

 species in which the lateral tooth is not developed, and 

 Say made his Alasmodon for the same section, Unio being 

 retained for species with both cardinal and lateral teeth. 

 We prefer keeping them together on account of their great 

 similarity of habit. Lately Dr. Troschel (in Wiegmann's 

 Archives for 1847) has attempted to found distinctions 

 between the several genera of Naiades on the characters of 

 the branchiae and lips. The peculiarities he describes in 

 his excellent paper do not appear to be more than 

 specific. 



The shells of this genus have frequently been used by 

 painters for containing their colours, and some of the 

 species furnish pearls. The animals are not eaten in our 

 country, but in the south of Europe, — where everything in 

 the shape of shell-fish is devoured with an avidity which 

 defies starvation as long as rivers and seas yield mollusca 

 in their present abundance — they are cooked for food, 

 either roasted in their shells and drenched with oil, or 

 covered with bread-crumbs and scalloped. 



