THE OYSTER. 189 



one, and the evidence is not of much value when only 

 a single bed is examined. The dead shells are swept 

 into the channel in some places, and covered up by 

 sand or mud in others, so that the dredge may come 

 up filled with shells when it happens to strike a bed 

 where they have been swept together, and in another 

 case, where most of the shells are buried, it may con- 

 tain few. If the dredge is heavy and is dragged with a 

 long line, it may dig into the mud and become filled 

 with old shells, where another dredge, or the same 

 dredge dragged in a different way, may contain few or 

 none. The contents of the dredge are determined by 

 so many accidents that single observations of the ratio 

 between shells and oysters are of little value, but the 

 case is different where a great number of dredgings is 

 made. In 1876 Mr. Otto Lugger visited most of our 

 beds, and measured the quantity of shells and of oysters 

 obtained from each. As he made a great number of 

 observations, his results give us a means of ascertaining 

 the average ratio in 1876. His results, obtained by the 

 examination of twenty beds, show that in 1876 the 

 dredge brought up 3 T %% bushels of oysters for each 

 bushel of shells. In 1878 and 1879 Lieut. Winslow ex- 

 amined in the same way seventeen beds in Tangier 

 Sound, and found that only 1^% bushels of oysters 

 were obtained for each bushel of shells. 



In November, 1882, we examined fourteen beds in 

 this way, and found that the average had fallen from 

 3^*5. in 1876 and I T 9 ^ in 1879 to I ^bushels in 1882. 

 Thirty-two beds were examined in the same way in the 



