18 ANIMALS INHABITING UNIVALVES. 



any exception, inliabit water, and liave only two horns ; the 

 eyes are placed at the root of the horns, or at some part of 

 their side, but never quite at the end or tip (p/. 5. /. 59) ; 

 several of tliesc animals are furnished with a cylindrical trunk 

 ar proboscis, at the end of which is the mouth furnished with 

 small teeth of a hook-like form, with which the animal pierces 

 (Tther shells, and then sucks the flesh of the inhabitants for its 

 food (p/. 10. /. 1). 



The family of Umaces without a breathing tube, of which 

 the Garden Snail is a familiar example, comprehends the re- 

 maining species of the genus Bulla and Voluta, and all those 

 of Trochus, Turbo, Helix, Nerita, Haliotis, Patella, and Chiton. 

 The water species have generally two horns, except the Chiton 

 and some Bulla. The eyes in some are placed on the head or at 

 the side of the horns ; but many of the animals have, besides 

 the horns, a short kind of column or pillar at the outside of 

 each horn (pZ. 9. /. 119. a), with the eyes placed at the tip of 

 Uiem, as in most of the Neritce. All the land species belong 

 to this family ; these have four horns, with tlie eyes at the tips 

 of the longest ; but none have the trunk or j^roboscis noticed 

 in the other family. 



OF THE SHELLS. 



Of the shells we may observe that the two valves or pieces 

 of which the Bivalves are composed are in general more or less 

 convex ; in a great number both valves are equally so ; in 

 many, one is more convex than the other ; but in some few 



