ANIMALS INHABITING UNIVALVES, 17 



LiniiEBUs ; they protrude neither tube nor foot beyond tlie sliell ; 

 the pallium is divided ; they have only one large muscle, whicli 

 in many species leaves a conspicuous mark on the interior sur- 

 face of the shell, as in the common Oyster, Ostrea edutis of 

 Linnaeus ; but in many others the mark is not discernible, as 

 in most of the Scallops. This family includes the genus Ostrea, 

 with the Scallops or Pectines, the Spondylus, a few Chamce, and 

 some of the Anomifv. 



The next natural division (the Mollusca with Heads of 

 Lamarck^ includes the animals inhabiting* the Jrgonauta and 

 the Nautilus, which are very little known, and appear to belong 

 or are nearly allied to the Sepia or Cuttle-fish. It comprehends 

 also the animals of the rest of the Univalves, including tlie 

 Chiton, if we except Dentalium, Teredo, and Serpula. This 

 division consists of two families ; one having a windpipe or 

 breathing tube projecting more or less beyond the edge of the 

 shell nearly on the back of the animal, through a hollow 

 groove or cavity, which may be seen at the end of the shell 

 furthest from the spire QjL 5./. 39. a); and the other without 

 any such tube, and consequently without anv hollow or notch 

 at the edge of the shell (p/. 9. /. 118 and 119. a). The animals 

 of this division are furnished with a head, and horns or feelers, 

 generally two eyes, and with teeth M'hich are very numerous 

 in some species ; they are all called Umax by Linnaeus. 



The genera Conns, Cyprcea, Buccinum, Strombus, Murex, 

 with part of the Bullce, and most of the Volutce, constitute the 

 family of Limacea with a breathing tube. These, with scarcely 



