LUTRARIA. 



GENERIC CHARACTER. 



Shell equivalve, inaequilateral, transversely oblong or 

 subovate, gaping at the extremities, particularl}' at the 

 posterior extremity ; cardinal teeth two, of which one is 

 doubled in the shape of a V, the other simple, with a large 

 deltoid cavity situated obliquely near the teeth; lateral 

 teeth none ; ligament internal, inserted in the cardinal ca- 

 vities, not visible when the shell is closed ; muscular im- 

 pressions two, lateral, remote, simple ; impression of the 

 mantle extending to the muscular impressions and having 

 a large and profound sinus extending nearly half its length. 



OBSERVATIONS. 



Lamarck separated this group from the Linnaian Mac- 

 trae, from which it is essentially distinct by the absence of 

 lateral teeth as w ell as by other less striking characters. 

 The animal has a large fleshy cylinder, containing two 

 tubes, one for respiration and the other evacuation, situated 

 at the posterior extremity. The foot is small and com- 

 pressed, placed at the opposite extremity or near it. 



It is a littoral genus, inhabiting estuaries and near the 

 mouths of rivers. 



Blainville unites this genus with Ligula Leach, under 

 the generic name Lltricola. Lamarck describes eleven 

 recent and one fossil species. 



PLATE IX. 



