ity of motion and apparent ease. In this case the revert- 

 ed foot of the animal is concave, and the surface of the wa- 

 ter within its circumference is compelled to a correspond- 



ing figure. 



REFERENCE TO THE PLATE. 



Fig. 2, back and front viewa ; natural size. 



LIMNEUS DECIDIOSUS. 



UESCRIPl ION. 



Shell oblong-subconic, acute : volutions five, convex, the 

 fourth and fifth small, the second rather large : suture well 

 impressed : aperture about equal to the length of the spire : 

 columella with the fold not deeply impressed : umbilicus 

 obvious, but verj narrow. 



SYNONYM. 



L. DECiDiosLSj S., Journ. Jlcad, Nat. S. vol. 2, p. 169. 



OBSERVATIONS. 



Several specimens were ]>resented to me by Mr. Au- 

 gustus Jessup who obtained them in Cayuga lake, New- 

 York and my brother B. iSay subsequently ascertained it 



PI. &5. 



