261 



OSTREAD^. 



This large and important family includes shells of very 

 various outline and sculpture constructed by animals pre- 

 senting considerable variations in the features of their 

 foot and mantle, but nevertheless having so many impor- 

 tant characters in common that we do not think it ad- 

 visable to subdivide the group. For though the foot in 

 Ostrea is obsolete the other characters of the animal of 

 that genus are such that we cannot place it in a distinct 

 group from Anomia on the one hand, or Placuna on the 

 other, through both which genera we have a very natural 

 transition into Pecten. The long fringes of the mantle in 

 Lima might seem to indicate a different family, but in 

 Lima spinosa we find them very short and associated with 

 ocelli as in Pecten, and in Limea * the mantle has no 

 tentacles. All the tribe have the mantle freely open, no 

 tubes, a small or obsolete foot probably capable in some 

 stage of the animal's existence of spinning a byssus, and 

 constantly doing so in some species, united adductor 

 mussels, leaving a single impression in the shells, and a 

 ligament wholly, or partly interior, lodged in a cardinal 

 groove, and sometimes accompanied with teeth. 



* Among the future additions to the Britisli Fauna will probably turn up 

 Limea Sarsii of Lciven, a shell which seems to be identical with the Lima oxissa 

 of the jEgean. 



