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 A HISTORY OF ESSEX year to year, so that what was common at one time may be rare at another, and particular species may have ceased to occur in one locality and have established themselves in another. In addition to the animals I have collected myself I give the Hydroids, Polyzoa, etc., collected near Harwich by Mr. S. P. Hope, lent to me by Mr. William Cole, and identified by Mr. Walter Garstang ; and those of various groups collected near Brightlingsea by Mr. H. W. Unthank, as described in his paper, ' Natural History Work at Brightling- sea,' published in the ^Journal of the Essex Technical Laboratories, No. 19, April, 1896, pp. 20610. These additions are more especially valuable because they give a number of species in groups of animals to which I have paid little attention. I also give a very complete and well- arranged list of the Mollusca drawn up by Mr. William Cole. In concluding this introduction I must express my best thanks to a number of friends who have assisted me in identifying the various species. These belong to so many groups, and my time has been so much taken up with other matters, that I did not feel confident in my own determina- tion. My thanks are especially due to Mr. Walter Garstang, who has examined and named many of the sponges, Ccelenterata, Nemertians, Chsetopoda and Polyzoa. Professor Herdman has assisted me in naming the Ascidians and Nudibranchs. The Rev. T. R. R. Stebbing has examined some of my crustaceans ; and my Sheffield friends, Professor Denny, Mr. Arnold T. Watson and Mr. E. Howarth, have assisted me over sundry animals. I hope therefore that on the whole the names are correct, but fear that some may not be, owing to the want of suitable specimens collected and preserved for this special purpose. The diffi- culties are also apparently increased by the probable existence of varieties differing from the recognized types, owing to local conditions and other causes. In several cases species which at one time were extremely com- mon and in some respects have been well preserved could not lately be procured for exact specific identification. I may also here say that in the Essex district some of the animals are abnormally small, as if dwarfed by unfavourable conditions. In some cases also only single specimens have been found, and it is uncertain whether they are full-grown animals. On the whole there are ten or a dozen doubtful identifica- tions. CHARACTERISTIC FEATURES OF THE COAST Before describing the various animals it seems to me desirable to give a short account of the chief characters of the coast, along the whole of which I have passed more or less frequently, since they must have such a great influence on the kind of animals found along it. My knowledge of the Thames is chiefly confined to the vicinity of Erith and Greenhithe, at both which places I lived on the yacht for some weeks in 1882. Though the free-swimming animals and plants are of much interest, the district cannot be looked upon as marine ; and I do not know exactly how far the influence of fresh water extends, 70