122 



some period subjected to a great degree of intestine mo- 

 tion while under so much confinement that the pebbles 

 could not move from their situations, and thus protected 

 the smaller shells that fell into the hollows between 

 them, while they were wearing away such as came in 

 contact with them. Some of the older shells are worm- 

 eaten, but no Serpula or Coraline has been found attach- 

 ed to them. 



OSTREA edulina? 

 TAB. CCChXXXYlU.-^Figs. 3 and 4. 



Spec. Char. Suborbicular or obovate; lower 

 valve rather concave, composed of undula 

 ting laminae ; the other smooth and flat ; 

 beak pointed, curved. 



Ostrea edulina? Ijam. Hist. Nat. 6. pt. 1. 218. 



A. smaller and much lighter shell than the last, although 

 often approaching it in form ; the great smoothness of 

 the flat valve and the want of straight lines on the sides 

 of the beaks will serve as distinguishing marks ; when 

 several are grouped together, they are apt to be much 

 elongated, and then come very near to O. tener, Min. Con. 

 252, of which however both valves are free from undula- 

 tions. 



Very abundant in beds and layers alternating with 

 fresh water shells, among dark coloured clay, forming a 

 thick stratum free from pebbles immediately below that 

 in which the last species occurs in the Sand-pit near 

 Woolwich. 



It is very probable that several species are included un- 

 der the name edulina by Lamarck of which this may be 

 one ; but it is doubtful and it will ever be difficult to ascer- 

 tain the point, the shells themselves are so variable. 



