Mr. Wilfrid Grenfell, the Superintendent of the Mission to Deep Sea Fishermen, has most kindly arranged to carry on a series of observations on the pelagic fauna and the fishes of the seas traversed by the Mission boats in the course of their work. The following report gives an account of the pelagic fauna collected in the North Sea during the early spring, and in the west of Scotland and Kinsale Harbour during the summer. The collections were preserved in picro-sulphuric acid and spirit, and were forwarded to Plymouth for examination. Owing to pressure of work, and to my leaving Plymouth somewhat unexpectedly, I have not been able to make a thorough investigation of all the collections, but have worked out the Copepoda with care, and have confined myself to short notes on the other species.

[The herring fishery is carried on at Plymouth during the winter months, when the adult herring seek the inshore waters for spawning. Besides these, however, the so-called “harbour herring” are taken in the summer and autumn; these appear to be the produce of the last spawning season, i.e. six months to a year old. Mr. Cunningham has shown me specimens taken in the Cattewater in May, 1889, which vary from 3½ to 5 inches in length. Those which are at present being brought to the Laboratory (September, 1890) are 9 or 10 inches in length, but their reproductive organs are still at an extremely early stage of development. Further observations on these harbour herring are much needed, and are being gradually made.

During the two years which I spent at Plymouth I collected a number of notes on the occurrence and distribution of the Hydroidea of the district, with the intention of giving a full account of the representatives of the group in the Plymouth area. My unexpected departure has prevented my carrying out this intention, but it has seemed to me worth while to publish my notes, fragmentary as they are, in the hope that they may be useful to my successors, and particularly because the list of the Hydroidea given in Part ii of the first series of this Journal is very imperfect. The list of species now given is incomplete, and had I had the time to search more closely for the inconspicuous and deep-water forms I should have been able to add largely to it. One species, which I only succeeded in obtaining twice, appears to be new to science.

This paper is intended to furnish a complete list of all the species of Opisthobranchiate Mollusca found up to this time by the Marine Biological Association at Plymouth, together with various notes upon their morphology and natural history. The Nudibranchiate section of the group has, however, already formed the subject of a preceding report published in this Journal, so that species which have not since been taken are recorded here by their names only, a fuller account of them being given in the previous report. All the species there recorded are distinguished in this paper by asterisks (*) affixed to their names. I have had the advantage of several works upon the classification of the group which have recently appeared, notably Carus's excellent Prodromus Faunæ Mediterraneæ, vol. ii, part 1, 1889; Bergh's Die cladohepatischen Nudibranchien (Zoolog. Jahrbüch., v, 1890; for a copy of this admirable work I am indebted to the author); and Norman's Revision of British Mollusca (Ann. Mag. Nat. Hist., VI, vol. vi, No. 31, 1890, pp. 60—91). I must also mention Vayssière's Recherches Zoologiques sur les Mollusques Opistobranches du Golfe de Marseille—I. Tectibranches (Ann. Mus. Hist. Nat. Marseille, Zool., II, 1885, Mém. No. 3) as having been of great service; and I regret that up to the time of going to press the second part of M. Vayssière's work has not arrived at the Laboratory, and I have been unable to refer to it.

On Plates I—VIII, for Journal Mar. Biol. ass. read Journal Mar. Biol. Ass.; for Planche read Plate; on Plates I—VI, for G. C. Bourne del read J. T. C. del.

Page 115, line 12, for Gadus æglefinus read Gadus merlangus.

Page 365, line 15 for Treorgy read Treorky.