Concerning the characters of the deep-sea Lamellibranchiates, Mr. Smith, in his report on the Lamellibranchia of the ‘Challenger’ expedition, says ‘very deep-water benthal species certainly have a tendency to be without colour, and of thin structure, no doubt resulting from the absence of light the difficulty of secreting lime, the scarcity of food and other unfavourable conditions of existence.’ But notwithstanding this, the same author continues: ‘The species are apparently few in number in comparison with those of shallow water; and new and peculiar generic forms which we naturally expected would have been discovered are of even still rarer occurrence.’ As in the group of the Lamellibranchia, so in the Gasteropoda, no very remarkable new genera or species have been found in deep sea. Some shallow-water genera, such as _Fusus_ for example, have representative species in the abyss; but, with the exception of a want of brilliant coloration and marking and a thinness of the shell, the deep-sea forms do not exhibit any characteristic features. One of the most brightly coloured shells found at great depths is that of _Scalaria mirifica_, which is tinted rose and white, but this seems to be quite an exceptional character among the deep-sea Gasteropods. Several new genera were found in the deep water, but their general characters do not call for any special remark. Among the Cephalopoda there seems to be little doubt that the genera _Cirroteuthis_, _Bathyteuthis_, and _Mastigoteuthis_ are entirely abysmal, and the same applies probably to one or two species of octopus; but as Hoyle remarks, ‘apart from the single fact that _Bathyteuthis_ and _Mastigoteuthis_ both have slender filiform tentacles with minute suckers, no structural features have been discovered which will serve to diagnose a deep-sea form from a shallow-water one.’ The exact habitat of the interesting genus _Spirula_ is unfortunately still unknown. In some parts of the tropics the shores are covered with spirula shells, and yet the animals that secrete them are still to be reckoned amongst the greatest rarities of our museums. The numerous dredgings of the ‘Challenger’ only brought to light one specimen of this animal, and that from a depth of 360 fathoms, and the ‘Blake’ caught one at a depth of 950 fathoms, so that there can be little doubt that _Spirula_ lives in deep water. [Illustration: FIG. 14.—_Bathyteuthis abyssicola._ (After Hoyle.)] It seems to be very probable that some day, when the right place and depth are discovered, _Spirula_ may be discovered in great abundance, but we have at present no means of judging whether this will be in very deep water or not.