CONCHIFERA OR BIVALVES. 73 



compressed, and the gaping of the shells in 

 most instances very inconsiderable. 



Family 5. — Mactridce* 



In this family the valves are equal, ge- 

 nerally gaping slightly at the sides, and having 

 the ligament placed in the interior. There 

 are 7 genera. 



25. Lutraria. — Shell equivalve, inequila- 

 teral, transverse; two 

 cardinal teeth in one 

 valve, and a trian- f { 

 gular pit ; no lateral ((vO* 

 teeth; a spoon-shaped 

 lobe, containing the 

 hinge. Animal similar to the Mactra. — 13 

 species recent, some of which are also fossil, 

 and 3 fossil only. 



Found in the sand at the mouth of rivers in 

 temperate climates. 



26. Mactra. — Shell oval, 

 transverse, with thin cardinal 

 and lateral teeth, one of 

 which is shaped like the letter 



* Les Mactracees, Lamarck. 



