PALATE OF CYCLASTOMA. 173 



Lymnsea is a large snail, whose shell, making six or 

 seven whorls, terminating in a fine point, is found in all 

 ponds and stagnant water, floating or gliding foot upwards, 

 and feeding voraciously on all kinds of vegetable matter. 

 The palate resembles that of the garden snail. 



PALATE OF PLANORBIS CORNEA. 



Planorbis is a flat snail with a shell in horizontal coils, 

 the size of a shilling, other species being smaller. The 

 tongue is oblong, and set with many rows of fine teeth. 



PALATE OF PALUDINA. 



Paludina is a remarkable fresh-water shell, more resem- 

 bling a large Periwinkle, but banded black and yellow, 

 with a strong operculum. It brings forth its young alive, 

 and they may be found in all stages of life in the space 

 between the mantle and the shell. The tongue of the Palu- 

 dina differs much from those of Lymnsea and Planorbis, 

 being long and slender, and the teeth like horny plates 

 laid over one another more like those of the land-snail, 

 Cyclastoma, and showing that it is, in truth, as La Mark 

 conjectured, the family which links the two great divisions 

 of land and water molluscs. Here then we have a very 

 interesting palate, and proof of the usefulness of microscopic 

 observation ; for nowhere but in the palate do we find the 

 very marked distinction between the Paludina and Lymnsea, 

 both inhabitants of the same stream, and at the same time 

 the close relationship to the little Cyclastoma, which lives 

 high and dry upon the chalky hills, and under the hedge- 

 rows of a limestone district. 



PALATE OF CYCLASTOMA. 



The Cyclastoma elegans has a white and finely striated 

 shell ; its palate should be mounted in fluid, as indeed all 

 these are. Simple salt and water well preserves them. 



