114 TEANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



animals are clinging to and entangled in the branches in 

 abundance, some parts give attachment to little tufts of 

 Calothrix, 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 

 Algae thought so much of by the eleveurs 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 (PI. II, fig. 

 5). This special Diatom used to be known as Amphi- 

 pleura, or Navicida, ostrearia, but its correct name is now 

 Navicula fusiformis, var. ostrearia. This 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. 



I also collected samples of the mud, sometimes of a dark 

 green 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 Algae, 

 and minute animals. Altogether, all the evidence I was 

 able to collect shows, I think, that the bottom of a claire 



