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 A HISTORY OF ESSEX is that few kinds of animals can establish themselves permanently, which is very unlike what occurs in other tidal estuaries in the county. TABLE IV Half flood and high Half ebb and low At Er'ith 1-4. 14*0 4 O At Greenhitbe 2"? 5'4 1-8 1-2 Mean of all per 10 gallons 6-6 I. PROTOZOA Noctiluca mlliaris. This varies greatly in numbers at different places and in different seasons. Sometimes there are few, but on one occasion I found that the average number in the water of Harwich harbour, from the surface to the bottom, was about 4,000 per gallon. II. PORIFERA (Sponges) The best locality in the county seems to be the creeks east of Walton-on-Naze. The following species have been identified, but probably others occur, which have been ob- tained in the Orwell. I. CALCAREA 1. Leucosolenia lacunosa, Johnston. Dredged in the Wallet by Mr. H. W. Unthank. 2. Leucosolenia botryoides, Ellis & Sol. Pin Mill on the Orwell ; also dredged in the Wallet by Mr. Unthank. 3. Sycon coronatum, Ellis & Sol. In the creek east of Walton-on-Naze and in the Colne. Mr. Unthank records it from the Wallet. 4. Sycon compressum, Auctt. The only place in the county where I have found this species is in the creek east of Walton-on-Naze. II. SILICEA I. Cbalina oculata, Pallas. Possibly all my preserved specimens have been collected just outside Essex, but it is almost certain that it occurs at Harwich and Walton. 2. Halichtmdria panicea, Pallas. This occurs in the Colne, but not abund- antly, and I think I have seen it near Harwich and at Walton. 3. Isodictya fucorum (Bowerbank). Dredged in the Wallet by Mr. Unthank. 4. Isodictya palmata ? (Bowerbank). Dredged in the Wallet by Mr. Unthank. 5. C liana celata (Grant). This sponge does some injury to the oysters. My friend, the late Mr. Fred. Wiseman, told me he had found that by keeping the shells dry for a time the sponges could be killed, and the oysters restored to a healthy state. I have found several other species not yet identified, and probably many more occur, since some seem to be very local, and not to be met with every year. III. CCELENTERATA (Jellyfish, Sea Anemones, etc.} I. HYDROZOA i. HYDROID ZOOPHYTES I have never made any effort to collect the more minute species, and the list would have been much more incomplete than it is if Mr. Wm. Cole had not lent me a collection made by Mr. Hope near Harwich, the species of which are distinguished by his name. They have been identified by Mr. Walter Garstang. 1. Coryne vaginata, Hincks. Taken by Mr. S. P. Hope in Essex waters near Harwich in June and July. 2. Syncoryne eximia. Off Brightlingsea (H. W. Unthank). 76