Between a and b there is another curved mass of transparent cartilaginous substance, along the bottom of which runs a spine to which is attached a fringe-like fin. There is a spine upon the back; the eye is very prominent and bright; upon the back, between the eye and the spine, there are successive stripes of purple and burnished gold, so that this little animal is one of the most gorgeously coloured denizens of the ocean. It swims about amongst the purple barnacles and pink nautili, seeking on the shores of these shining islands its prey, the curious formation of its mouth being admirably adapted to enable it, whilst swimming under these painted floating islands, to crop off what it lists. There were scarcely any gelatinous animals in the sea this day; but many Janthina shells and Velella were round the ship, to which were attached barnacles of different species; amongst this group of islands numerous crabs were swimming about and running over them. Animals resembling a wood-louse were also in the sea, swimming and running about the floating shells and barnacles. We caught also a new species of Janthina, the float of which, instead of being nearly round and extending over the shell on each side, was spread like a spiral fold from the shell; the breadth of this fold was 0.45 inch, close to the mouth of the shell, and it gradually tapered off to a point, its length being 3.6 inches. This float being curved round like the tail of an animal, the whole thing bore the appearance of being a sort of snake, of which the shell was the head; the sailors called them caterpillars before I had examined them. The float was composed of two parts, one of which was only froth and the other was apparently some extraneous substance attached to the froth. The shell is very different from those of the other nautili in being much more deeply indented with circular striae. July 18. South latitude 19 degrees 49 minutes; west longitude 3 degrees 10 minutes 15 seconds. We have lately caught several specimens of Creseis. Each consists of a cylindrical tube, increasing in size from its broadest extremity to the centre where it is thickest, and decreasing from the centre to its other extremity, where it becomes a fine point. It is throughout its extent gelatinous, transparent, and of strong consistency. There is apparently a valve at its broadest extremity. Length 1.1 inch. Breadth in centre 0.1 inch. Breadth at mouth of wide extremity 0.08 inch.