MARINE ANIMALS ON THE ESSEX COAST. 23 



localities. In some places the water is much more muddy than 

 it used to be. Another probable cause of change in the estuaries 

 is the improved draining of the land, which necessarily tends to 

 increase the amount of fresh water at the time of floods. I have 

 been told of a case in which such an event killed thousands of 

 pounds worth of oysters, and this effect would explain why so 

 many full grown shells of clams and other species are often seen 

 farther up the rivers than living ones now occur. It is, however, 

 very difificult to believe that this cause could operate in the case 

 of comparatively open water. It is, of course, easy to under- 

 stand that a permanent diminution of fish may have resulted 

 from over fishing, and we may well believe that the great 

 number of fish, shrimps, and star-fish caught, and the various 

 operations of oyster culture, may materially affect the number of 

 some other animals ; since the inter-relations of those living 

 together are probably sufficiently intimate to produce such an 

 effect. We must also bear in mind possible cyclic changes in 

 the weather, and the effect of a series of hot and cold, dry and 

 wet years. 



Though thus calling attention to various possible explana- 

 tions of the facts I have described, I feel that they are little 

 better than suggestions, and that possibly the final results may 

 be due to the variable combined effect of many such temporary or 

 permanent causes. It seems to me very desirable that those who 

 have constantly studied other districts should record their experi- 

 ence, since that might throw far more light on the question, and 

 eliminate various sources of error which beset this subject on all 

 sides. 



Note. — For the identification of the species named in this 

 paper, I am to a great extent indebted to Mr. Walter Garstang, 

 the Rev. T. R. R. Stebbing, F.R.S., and Professor Herdman, 

 F.R.S., so that I believe they may be relied upon as correct. 



