210 Fresh-Water Shells. 



The surface, undei' the magnifier, appears beautifully checkered 

 with minute, revolving, and longitudinal lines, v/hich are also a 

 little -waved. Sometimes there are one or more whitish, opaque 

 bands, as if scratched by the mantle of the animal. The thicken- 

 ing of the lip is found only in old specimens, and in these also 

 there is a broad layer of pearly enamel reflected over the columella, 

 Avhich has also a very prominent fold. 



The animal is olivaceous, surface very smooth and silky ; the 

 foot is kite-shaped, longer than the shell, terminating in an acute 

 point ; expansions each side of the mouth acutely angled ; ten- 

 tacula olivaceous above, light ferruginous beneath, long and 

 threadlike. The pointed lobes of the mantle are very conspicuous. 



The motions of the animal are very rapid, and it seems to move 

 with equal fjicility in an inverted posture, at the surface of the 

 water. 



The ova are excluded, enveloped in a gelatinous substance, 

 about twelve or fifteen in number, and of an egg-shaped form. 

 In about a fortnight they escape from the jelly, and move about 

 with great rapidity. In fact, they are seen in motion for some 

 time previous, apparently struggling to disengage themselves from 

 their nidus. 



This shell is everywhere to be found. . Scarcely a brook or 

 pool is met with but some of these shells will be found in it. It 

 is more especially to be found in the running brooks. 



The difference between this and 'F.fontiiidlis of Europe, is very 

 slight. The spire may be a little more prolonged and acute. 



It is interesting to keep a number of them in a vessel of water 

 and observe their motions and habits. The manner in Avhich they 

 open their mouths and display the lingual organ, — the manner in 

 which tliey rise to the surface and open the air cavity, into which 

 its structure permits no water to enter, — and above all, the beautiful 

 and unaccountable manner in which it glides along, will never 

 fail to excite astonishment. They feed freely upon any kind of 

 vegetable. 



We have here an instance of the inLerrnirable chain of existen- 

 ces, and of the subserviency of one animal to another. And it is 

 curious, too, that, in general, w'e have the power to elude or 

 subdue animals of greater strength and magnitude than ourselves, 

 much better than we can those which are inferior to us. On 

 looking carefully about the neck of the animal of this shell, we 

 find him beset with numerous little things looking like short, 



