VARIETIES OF OYSTERS. 145 



poisonous, and Mr. McAndrew informs me that the 

 captain and some of the crew of his yacht were suddenly 

 taken ill at Vigo, after having eaten some fine Anomice, 

 which looked to them temptingly like oysters. (j) 

 The muscle of attachment appears to have an excavating 

 or eroding power, like the foot of a limpet or other boring 

 mollusc. 



When an Anomia is fixed to the shell of an oyster, the 

 lower part of the plug is sunk below the level of the sur- 

 face, and is separated from it by a kind of sloping ditch. 

 This gives a stronger hold, and the base of the plug is 

 often spread out, so as to increase the fulcrum. 



The structure of the plug is very remarkable. It is 

 composed of perpendicular plates, which are alternately 



(j) In his "History of the Oyster," p. 26. (London: Van 

 Voorst, 1858) Professor T. C. Eytonsays: 



" The Rock Oyster, Anomia, is not bad eating. I was particularly 

 struck with the size of those I found in Glengai iff Bay, on the West of 

 Ireland. 



I believe that Delle Chiaje is right, when he says that the Mussel 

 and Oyster are poisonous in summer; and probably this is the case 

 more or less with all shell-fish that have spawned, or are just about to 

 spawn, and that those which, when out of season, are sold in- the Lon- 

 don market, are not fit for food. I have seen the effects of eating out 

 of season mussels, which cause great derangement in the system ; but 

 I have not seen anyone made ill by oysters, although the same effects 

 might be expected, and occurred at Havre. The ' Green Oyster,' 

 formerly in such high repute, is now gone out of fashion, and those 

 with white beards are esteemed the most. The green colour at Burn- 

 ham, Mr. Sweeting informs me is imparted by a species of diatom 

 growing on the beds , this is probably not unwholesome : but there is 

 another green oyster, found on some portions of the Welsh coast, 

 which I should most decidedly think was ; it is said to be coloured 

 with copper from the mines." 



