LIMNEANA. MOLLUSC A. PHYSA. 213 



The difference between this and P. fontinalis of Europe, is very 

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



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

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

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

 which they 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 interminable chain of existences, and 

 of the subserviency of one animal to another. And it is curious, too, 

 that, in general, we 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, minute, white lines, which are, in truth, 

 little parasites {Gordius inquilinus, Miill.) attached like leeches, and 

 which derive their nourishment from the fluids of the animal, without 

 his having the power to dislodge them. 



Physa ancillaria. 



Shell ovate-globose, pale-yellounsh ; whorls four, smooth; suture 

 not impressed ; aperture nearly as long as the shell. 



Figure 142. 



State Coll., No. 74. Soc. Cab., No. 1308. 



Physa ancillaria, Say ; Journ. .lead. J\''ai. Sc , ii. 124. 



" Shell heterostrophe, sub-globose, pale-yellowisb ; whorls 

 rather more than four, very rapidly attenuated ; spire truncated, 

 hardly elevated beyond the general curve of the surface ; suture 

 not impressed ; aperture but little shorter than the shell, dilated ; 

 labium a little thickened on the inner sub-margin." (Say.) 

 Length |i inch, breadth ^^ inch, divergence 90°. 



Found in Connecticut and Merrimack Rivers, Fresh Pond, &c. 



Animal of a bright lemon-color. 



This shell is distinguished from the preceding by its much shorter 

 spire, more angular outline, and especially by its suture, the margin 

 of one whorl being so closely and perfectly applied to the pre- 



