236 MONOMYARIA.—OSTREADA. 
ciently abundant to pay for dredging. The sea- 
oyster is often, before being brought to market, 
kept for a time in artificial beds, in order to improve 
its flavour. 
‘“‘'The most esteemed oysters are those of the 
small ovate, but deep-shelled variety, called Natives, 
among which, those of the river Crouch, or Barn- 
ham Oysters, are pre-eminent for the marine 
flavour; probably on account of the facilities for 
rapid importation of them in fine condition. Much 
of the quality depends on the ground and condition 
of the beds: the oysters of different years from the 
same place often vary materially in this respect. 
They are considered full-grown for the market 
when from five to seven years old; sea-oysters 
at four years. The age is shown by the annual 
layers of growth, or ‘ shoots,’ on the convex valve. 
Up to three or four years, each annual growth is 
easily observed, but after their maturity it is not 
so easy to count the layers. Aged oysters become 
very thick in the shell. In the neighbourhood of 
fresh water the oyster grows fast, and improves in 
body and flavour. The flavour is said by some to 
improve by shifting the oysters as they approach 
their full growth. Frost kills numbers, and when 
they are left dry at low ebps, the run of fresh 
water from the land turns them, what is called, 
‘foxy, of a brownish red colour. ‘They are some- 
times seized with sickness during the spawning 
season, and considerable numbers may die. Much 
labour is required to keep the beds in good order, 
cleansed from shells and rubbish, star-fishes, bar- 
nacles, corallines, and sea-weed, which grow freely 
in the spring of the year. On the cleanliness of 
the ground the prolific character of the bed, if the 
