GENUS XXI. CYPRjJSA. 101 



membrane on each side of the animal, wliich it extends over 

 the sides of the shell, meeting near the back. 



These shells are not covered with a periosteum as most 

 are ; they have no operculum. 



Linnaeus describes 44 species, Gmelin has added 70, and 

 Dr. Turton 6. Total, 120. 



Both Adanson and Lamarck make this a distinct genus, 

 without any alteration. 



Lamarck describes it as follows : 

 Cyprjea. Shell oval, convex, the edges rolled inwards ; the 

 aperture longitudinal, straight, and toothed on both sides 

 (see Cyprcea Caput serpentis Linn. /. 61. Z>). 



