442 J. H. OETON. 



Another suggested means of combating the spread of Crepidula is 

 one which might be put into practice at once, if it has not already been 

 adopted, namely, that of encouraging dredgers to bring in the whole of 

 their catches of Crepidula and to destroy them. Possibly, also, some- 

 thing might be done by transplanting enemies of Crepidula into the 

 oyster district, but great care should be taken that the enemies of 

 Crepidula should not turn out to be also enemies of oysters. 



The slipper-limpet, however, is not the only animal on the dredging 

 grounds which is an enemy to the oyster. Sea-squirts, other bivalves 

 than the oyster, many worms, barnacles, and all other animals which 

 feed on the material found on or floating near the sea bottom, are like- 

 wise enemies of the oyster, enemies in the sense that they compete for 

 food and space. On the other hand, there may be quite enough food on 

 the sea bottom to support all these animals and many more, but at 

 present we have no definite information as to how much of this kind 

 of food there is, although there would seem to be plenty for all. 



In the question of how to treat Crepidula, therefore, it would be of 

 great value to have some precise information as to how much oyster 

 food there is on or near the sea bottom, and it is to be hoped that before 

 long the desired information will be obtained. 



It has been stated that the presence of Crepidula on oyster grounds 

 is evidence that the grounds are healthy, and there can be no doubt 

 now that this is true, since Crepidula takes the same food as oysters. 

 An interesting confirmation of this statement lies in the fact that 

 inshore Crepidulae at West Mersea are much finer than the specimens 

 obtained on the outer grounds, and it is well known that the inshore 

 oyster grounds are much healthier than those outside. 



The substance of this report may now be summed up as follows : — 



Crepidula feeds on the same kind of food as oysters, and its presence 

 on oyster grounds may therefore be taken as evidence of the grounds 

 being healthy. 



Crepidula takes special care of its spawn. Since all the male 

 Crepidulae change into females, every individual produces in its later 

 life at least 13,000 eggs per year. 



The eggs develop into free swimming larvae, which may be scattered 

 far and wide. 



Whether Crepidula is harmful to oysters cannot be determined until 

 some measurements have been made of the actual amount of food on 

 the sea bottom, excepting in cases where it occurs in such quantities 

 as to smother the oysters. Crepidula as an enemy to oysters must be 

 put in the same class as the mussel. 



There are two main problems to be attended to. 



