IN THE UISTRIUT OF THE THAMES ESTUAE.T. 435 



•i. iV. pelagica, Linn.— At one time was common off Harwich 



amongst the sandy tubes built by Sahellaria spinulosa, 



Lamarck. 

 5. N. cultrifera, Grube. — Common in the mud at low water 



in particular localities, especially at the mouth o£ the 



Colne and off Harwich. 



When moixnted in balsam these species can be at once distin- 

 tinguished from one another by the following characters : — 



1. N. diversicolor. — Numerous small black prickles about the 



head. 



2. N. Dumerilii. — Unusually long tentacular cirri. Eyes black 



and very large for the size of the animal, those of each 

 pair very close or even partially coalesced. Prickles 

 almost or quite invisible. 



3. Hr. loiigissima. — Prickles very obscure or invisible. Eyes 



pale brown by transmitted light. Tentacular cirri short. 

 Jaws dark-coloured, with rounded teeth. 



4. N. pelagica. — Numerous prickles of varying size and some- 



what rounded shape, of pale brown colour by transmitted 

 light. 



5. JSf. cultrifera. — Unusually large black angular prickles. 



Many small blood-vessels perpendicular to the length of 

 the parapodia. 



One great advantage of these characters is, that they apply 

 equally well to the Nereis and Heteronereis state, and can be 

 seen at once without injury to the specimen. 



I have found only one specimen of N. longissima in the Nereis 

 condition, obtained in the mud of the Orwell at Pin Mill, which 

 is 7 inches long and over | inch thick. When put into diluted 

 formalin, it broke itself into two, which I never knew happen in 

 the case of any other species. I have seen and caught it in the 

 Seteronereis condition on only two occasions. The first was off 

 Sheerness, in the evening of May 11th, 1882. I saw round the 

 yacht large numbers of what I thought were small red fish swim- 

 ming near the surface at the rate of several miles an hour ; and, 

 on catching some, was astonished to find they were worms about 

 4^ inches long. On putting some into my large aquarium, a small 

 Fandalus seized one two or three times as large as itself and 

 carried it down to the bottom. The second occasion was late in 



