AURICULACEA. 169 



The third constitutes a group of considerable importance, 

 intermediate between the two families, the Auriculacea and 

 the 'Lyimimana, and partaking ecjually of the characters of 

 both. The members inhabit chiefly the vast rivers of South 

 America, but more especially La Plata ; — 



" Tlie sea-like Plata, to whose dread expanse, 

 Contiguous depth, and wondrous length of course. 

 Our floods are rills." 



Different genera of the second family present, therefore, 

 familiar instances of diversified locality and restricted 

 haunts ; no one ever trenches on the dwelling-place of 

 another. Such as remain contentedly in stony places, or 

 among the roots of trees, have no wish to roam beyond 

 their precincts : they neither covet the favourite locality 

 of the marsh-marigold and bright blue mouse-ear, nor yet 

 the ample waters of those sea-like rivers which sweep 

 onward in their silent dignity through the plains of the 

 New World. 



The shell of this family is much more solid than that of 

 the preceding, and is mostly coated with a stout epidermis, 

 beneath which the animal frequently deposits some variety 

 of colouring. 



