Mothcr-of-Peavl Shell. loi 



bottom was thoroughly cleaned, this fact, if the 

 above explanation be correct, would point to a far 

 more rapid growth of oyster shell than pearlers have 

 hitherto thought possible. 



It is often maintained in Australia, that as 

 certain spots are left at the end of one season, rich 

 in shell, and six months afterwards the identical 

 spots are found bare, the oysters must possess the 

 power of migrating at will. There is, however, no 

 evidence of value to lead to such a conclusion, 

 Tind the inference from the disappearance of shells 

 is, that some change has taken place at the bottom 

 of the sea, the shells having been probably buried 

 by sand or mud, which doubtless is continually 

 shifting, especially where the tides are strong and 

 the sea shallow. 



The geographical distribution of the true Mother- 

 of-Pearl shell is confined to the Pacific and Indian 

 Oceans and their connecting seas. Cape Horn, and 

 the Cape of Good Hope stretching away down 

 into cold latitudes, appear effectually to have pre- 

 vented their successful migration in the present age, 

 by any favouring current to the Atlantic. 



The ancient history of the Mollusca, as told 

 by Geology, is well worth studying. The Lamelli- 

 branchiata or Conchifera, existed as far back as the 



