THE POUCH-SHELL. 



337 



the muzzle. In one respect, the Ampullaria seems to be a connecting link between the gill- 

 bearing and lung-bearing mollusks, being said by high authorities to possess a pulmonic or 

 lung sac, in addition to its gills. 



POND-SNAIL.— Limncea starjualis. (Natural size.) 



In the accompanying illustration the common Pond-snail, or Lijin^ea, is shown in the 

 act of climbing up the stem of a water-plant. In all the members of this family the shell is 

 thin, and sufficiently capacious to con- 

 tain the entire animal when it desires 

 to withdraw itself into its home. The 

 aperture is simply rounded, without 

 notches or ridges, and the lip is sharp. 



In the water-glass of the illustra- 

 tion will be observed the pond-snail, an 

 equally common European shell, called 

 from its flattened whorls the Planoiip.is. 

 In this animal, the foot is short and 

 round ; the tentacles are long, slender, 

 and leave the edges at their inner bases. 

 Both this and the preceding species are 

 in the habit of burying themselves in 

 the mud during a drought, and there 

 passing a semi-torpid existence. 



A very remarkable species, called, 

 from its peculiar shape, the Fresh- 

 water or River Limpet (Ancylus la- 

 custris), is found in various parts of 

 America, Madeira, and some portions of 

 Europe. It inhabits swiftly running 

 streams, and is mostly seen attached to 

 stony and aquatic plants. Although 

 the shell is so limpet-like, the animal 

 does not partake of the resemblance, 

 being very like that of the pond-snail, 

 and having triangular tentacles with the 



eyes at their bases. The generic term, 

 Ancylus, is of Greek origin, and signi- 

 fies a small round shield or target. 



The little elongated Pouch-shell, a species of a rather small genus, extending over the 

 greater part of the globe, is thin, spiral, polished, and the aperture is rounded in front. In 



Vol. m.— 48. 



PLANORBIS — Flaiwrbis Cornells. (Natural size.) 



