24 M. Kroyer on the Danish Oyster-Banks. 



examination of the position of the oyster-banks of Jiitland and 

 Schleswig does not confirm the idea that oysters flourish more 

 especially at the mouths of rivers. M. Kroyer very correctly 

 remarks, that we are not to regard oyster-banks as elevated 

 portions of the submarine land, or as rocks or sand-banks, &c., 

 to which the oysters are attached by their valves ; but merely 

 to understand by them those parts of the bottom of the sea on 

 which oysters occur in large numbers. Where the submarine 

 land consists of rocks and loose stones, the oysters adhere 

 partly to the projecting portions of the rocks and to the sepa- 

 rate stones ; but many likewise lie loose on the bottom : the 

 latter is, of course, always the case when the bottom consists 

 of loam, sand, or mud, except when several have grown toge- 

 ther in irregular heaps of three, four, or five individuals. More 

 than five or six are not united ; because, were they to grow 

 together in too large masses, the lowest would be prevented, 

 not only from being developed, but likewise from opening their 

 shells. It is likewise not correct that they always rest on the 

 valve which is turned downwards. The circumstance of a 

 much larger number of young individuals not being met with 

 on the banks of Denmark, the author is inclined to attribute 

 to the numerous enemies of the oysters, of which the worst are 

 the voracious sea-stars Cliona celata of Grant is so far pre- 

 judicial to oysters, that its groups penetrate the shells, and 

 pierce holes in them, thus rendering them soft and brittle, so 

 that their inmates are deprived of their protection, and more 

 exposed to their enemies. Such pierced oysters are also not 

 willingly taken by dealers, as they are easily broken in the 

 packing. The author discusses the circumstances that are 

 favourable and unfavourable to the prosperity of oysters, and 

 states, as the place best adapted for their development, a flat, 

 firm bottom, at a depth of from five to fifteen fathoms, where 

 the current is not violent. Too strong a current carries away 

 the young brood : a flat bottom, and an inconsiderable depth, 

 facilitate the fishing. 



The second part treats of the Danish oyster-banks in parti- 

 cular. The term Danish is employed in the Danish sense, in- 

 asmuch as the banks of Schleswig are included under it, the 

 oysters from which are known throughout Northern Germany 



