60 
animals are clinging to and entangled in the branches in 
abundance, some parts give attachment to little tufts of 
Calothriz, while nearly everything is covered with innu- 
merable Diatoms or their remains, such as Gomphonema 
stalks adhering to the stems of Cladophora. 
Probably so far as oyster culture is concerned the green 
Alge thought so much of by the éleveurs are only of 
importance as forming points of attachment and shelter, 
or favourable environment, for the microscopic forms of 
life and especially for the Diatoms. It is known that under 
all conditions natural and artificial, Diatoms form a most 
important constituent of the food of the oysters, and it has 
been established by several eminent investigators that the 
green (or rather greenish blue) tint of the Marennes 
oysters is due to the presence in the ‘‘claires”’ of a par- 
ticular kind of Diatom in enormous profusion (Pl. I, fig. 
5). This special Diatom used to be known as Amphi- 
pleura, or Navicula, ostrearva, but its correct name is now 
Navicula fusiformis, var. ostrearia. his form is found 
in our own district in the estuary of the Dee, although not 
abundantly; but it is probable that there are many other 
kinds of similar Diatoms that would do equally well for 
rearing and fattening oysters on, and as a matter of fact 
the contents of an oyster’s stomach show that the food has 
consisted of various kinds of Diatoms (in one case 87 
species were found) as well as other lowly organisms. 
T also collected samples of the mud, sometimes of a dark 
ereen colour or almost black and sometimes browner, from 
the bottom both of dry and wet claires, and on submitting 
these now to a detailed microscopic examination I find 
that the deposit is very largely composed of organic parti- 
cles, such as living and dead Diatoms, spores of Alge, 
and minute animals. Altogether, all the evidence I was _ 
able to collect shows, I think, that the bottom of a claire 
