MOLLUSC A OR UNIVALVES. 139 



Order II. 



GASTEROPODA.* 



Some of the animals of this order have no 

 shell ; others have a dorsal shell not enveloping 

 them ; and others, again, have one more or 

 less hidden in the mantle. The body is straight, 

 not spiral, having a foot united to it nearly 

 the whole length, and used for creeping. They 

 are divided into eight families: — 1. Tritouidce. 

 2. Dentalidce. 3. Phyllididce. 4. Semi-phyl- 

 lididce. 5. Calyptrceidce. 6. Bullceidce. 7. Ajply- 

 sidce. 8. Limacidce. The seven first live in 

 the sea, the last on land. , 



Family 1. — Tritonidce.'\ 



The Mollusca which form this family have no 

 shell, either external or internal. The body is 

 long, and the respiratory organs distinct and 

 placed above the mantle, either on the back or 

 sides. They are all marine : six genera. 



* Les Gasteropodes, Lamarck, 

 f Les Tritoniens, Lamarck. 



