ANODONTA. CONCHIFERA. 89 



side, and reflecting tints like the colours of the rainbow. 6 in- 

 ches long. Inhabits tropical rivers Lam. vi. 1, 89. 



Gen. 5. ANODONTA, Lam. Mytilus, Lin. 

 Shell equi valve, inequilateral, transverse ; hinge linear, without 

 teeth ; a glabrous plate, truncated or forming a sinus at its 

 anterior extremity, terminating the base of the shell ; two se- 

 parate lateral muscular impressions ; ligament linear, exterior, 

 sunk in the sinus at its anterior extremity. 



The shells of this genus are usually thin and nacreous, and they are covered ex- 

 ternally with a thin brownish-green epidermis. The umbones are oblique, partly 

 directed to the posterior side, and always decorticated. They are found in ponds 

 and lakes, where they bury themselves more or less deep in the mud at the bottom. 

 The animal has two short tubiform openings, formed of the posterior extremity of 

 the mantle, furnished with tentacular filaments. The Anodontae have no byssus, and 

 they use their large compressed, rounded, and muscular foot to execute their move- 

 ments. They are hermaphrodite and viviparous. 



A. cygnea, Lam. Shell transversely ovate., convex, brittle., rather 

 compressed on the anterior side ; furrows transverse, unequal ; 

 hinge lateral ; epidermis brownish green, and the shell beneath 

 silvery. 6 inches broad, and 2<| long. Inhabits ponds and lakes 

 in Europe. B Penn. Brit. Zool. iv. pi. 70. 



A. anatina, Lam. Shell transversely oval, brittle, rounded behind, 

 subangulated before ; transverse furrows unequal j margin mem- 

 branaceous; colour pale or yellowish green, with darker rays* 

 3^ inches broad, and 2 inches long. Inhabits fresh waters in Eu- 

 rope. B Penn. Brit. Zool. iv. pi. 7L 



A. Pennsylvania a, Lam. Shell ovate, convex depressed, fragile, 

 umbones prominent ; inside bluish silvery. 2 inches broad. In- 

 habits rivers in N. America Lam. vi. 1, 86. 



A. exotica, Lam. Shell ovate-oblong, transversely sulcated, poste- 

 rior base angular ; umbones prominent ; inside brilliant silvery. 

 8 inches broad. Inhabits rivers in India. Lam. vi. 1, 87- 



A. Patagonica, Lam. Shell subovate, angular before, compressed 

 and carinated towards the umbo, with concentric transverse striae ; 

 sides rounded. 3 inches broad. Inhabits S. American rivers. 

 Lam. vi. 1, 88. 



Gen. 6. HYRIA, Lam. 



Shell equivalve, obliquely trigonal, auriculated, with the base 

 truncated and straight ; hinge with two spreading teeth ; the 

 posterior one divided into numerous diverging portions ; the 

 anterior or lateral tooth strong, elongated, and lamellar ; li- 

 gament linear, exterior. 



H. avicularis, Lam. Umbones smooth ; epidermis greenish brown, 

 with fine transverse striae ; auricles terminated in points, the 

 posterior one much elongated. 3 inches broad. Lam. vi. 1, 82. 



Gen. 7. UNIO, Lam. Mya, Lin. 

 Shell transverse, equivalve, inequilateral, free, with the umbones 



