The group of the Annelida is not very well represented in the deep-sea fauna. The genera _Serpula_ and _Terebella_ have been found very widely distributed over the earth, at all depths from the shore to the abyss, but there do not seem to be many genera that are confined to deep water. In some cases, where there is a scarcity of lime in the water, the thin protecting tubes of the sedentary forms are strengthened by the adhesion of foreign particles, such as sponge spicules and arenaceous foraminifera, but in others, the tubes are formed of successive layers of a transparent quill-like substance (_Nothria Willemoesii_) which is frequently armed with spiny projections. Most of the errant Polychætes found at great depths are said to be most brilliantly coloured, and some of these, such as _Eunice amphiheliæ_, have the power of emitting a bright phosphorescent light; but there seem to be no very definite and constant characters separating these forms from the Polychætes of shallow waters. As is the case with many other orders of animals, the species of Annelida living in deep water are either blind or possess eyes of a remarkably large size. _Genityllis oculata_ may be taken as an example of a deep-sea annelid with large eyes. This annelid, belonging to the family Phyllodocidæ, was found at a depth of 500 fathoms in the Celebes sea. It possesses two enormous eyes which cover almost the whole of the head, and there can be no doubt, from the investigations of Dr. Gunn on their minute anatomy, that they are perfectly functional. Before leaving the Annelida a brief notice must be made of the very extraordinary form _Syllis ramosa_, found parasitic on a hexactinellid sponge at depths of about 100 fathoms. It is chiefly remarkable for the very complicated manner it has of producing buds which do not immediately become detached from the parent, but form a compound network which ramifies through the interstices of the sponge like the colony of a Hydromedusan. Passing now to the sub-kingdom Mollusca, we shall find that all the classes are represented in the abysmal fauna. The Lamellibranchiata, or bivalves, occur in almost all depths of the ocean, _Callocardia pacifica_ and _Callocardia atlantica_ having been found at the enormous depth of 2,900 fathoms. Some species, such as _Venus mesodesma_, have a very wide bathymetrical distribution, but others are only known to occur in deep water.