229 



Fam. 5. 



Animal with an elongate foot, a more or less 

 conical spiral body, a short muzzle, with dilated 

 lips and compressed tentacles, with the eyes 

 near their outer base : the mantle, which covers 

 the body, has a thin edge and is protected by a 

 variably shaped pale uniform-coloured shell, 

 which is clothed with a hard olive periostraca. 



They live in ponds and ditches, often floating on 

 the surface of the water, their back downwards, or 

 crawling on the mud at the bottom, or on aquatic 

 plants, but always coming to the surface to respire. 



These animals were scattered about by the Linnaean 

 conchologists among the Helices, the Turbines, the 

 Bullce, the Nautili, and the Patellce, because their shells 

 vary considerably in their shape and form. They 

 form, however, a most natural group, from their having 

 very similar animals. Like water-plants, they are 

 distributed very widely, and are to be found in al- 

 most all parts of the world. 



It had been supposed that the shells of fluviatile Mol- 

 lusca could be distinguished from those of the terres- 

 trial kind, by the edge of the mouth of the shell never 

 being furnished with a thickened internal rib, and not 

 being in the slightest degree reflexed, and that the 

 animal never closes it with an epiphragm ; however, 

 further examination has shown that when the Pond- 



