Fresh-Water Shells. 205 



side are four volutions, distinctly separated by tlie suture, wliicli 

 are carinated, and form a shallow, salver-sliaped depression ; the 

 whorls enclose each other in a very regular spiral to the last fifth 

 of the outer one, when there is a sudden enlargement and distor- 

 tion towards the left, by which a large, bell-shaped throat is 

 formed ; aperture also dilated, and strongly angular on the left 

 side ; within glazed, reflecting light-blue and brown ; surface 

 regularly marked with fine, transverse, raised lines, and interven- 

 ing grooves. Greatest diameter I inch, at right angles with this 

 I inch, small diameter -i inch. 



This shell does not attain the size of the preceding species ; and 

 when mature, its dilated throat distinguishes it from every other 

 known species ; and the remarkable manner in which it is turned, 

 as it were by violence, so as to look to the left, is a still further 

 distinction. The outer whorl is everywhere of the same breadth ; 

 and the immature shell, before the dilatation of the throat, mav 

 be known by the very regular enrolment of the whorls, and the 

 very contracted aperture in consequence of the verv unequal 

 diameters. 



Planorbis Aumigerus. — (Say.) 



^^ Shell small, brownish horn-color, or light, 

 ^ ^^ chestnut, orbicular; right side nearly 2:)lane, 

 H with only a slight central pit, showing four 



rounded volutions, distinctly separated by the 

 suture ; left side deeply concave, exhibiting all the whorls, which 

 on this side are sub-carinated ; surface shining, faintly marked by 

 the liufcs of growth, and on the left side, may be distinctly seen 

 several raised revolving lines on each of the whorls; aperture 

 slightly inclining to the left, rounded, and very slightly modified 

 by the carina, very oblique ; edge of lip dark-brown ; at some 

 distance within the throat are five white teeth, nearly closing the 

 passage ; a large, prominent, oblique one is situated on the side of 

 the preceding whorl, and may always be seen ; a very small one 

 is by its side ; opposite to them are the three others which are 

 small. Larger diameter ^\ inch, smaller diameter -J^- inch. 



Animal very active, of a blue-black or slate-color ; foot long 

 and narrow. The shell is carried inchned at an angle of 45°. The 

 respiratory groove is very acutely pointed. 



Found abundantly in shady, stagnant pools and ditches, in 

 which an abundance of decaying vegetable matter is immersed. 



