The top of the head is divided into two prominent knobs, one on each side, which, viewed through a microscope, appear to be minutely reticulated.
The animal may be considered as consisting of four portions: the head; the upper part of the body, 0.18 inch in length, and divided into five rings; the lower part, consisting of one shield-like portion, 0.12 inch in length, the body at the lower portions of this decreases almost to the thickness of a thread; the tail, 0.3 inch in length, and divided into three shield-like pieces, laid one over the other as in the shrimp (imbricated); at the lower extremity of each of these scales there is on each side a fin-like leg, in addition to those above-mentioned.

Breadth of the animal across its head, 0.2 inch, and this was the broadest part of it.

It lived for some time out of water, and even when put into spirits, it swam in an extraordinary manner, falling head over heels every time, which motion it accomplished by swimming on its back and making rapid strokes with the fin-like legs with which it is provided behind.
We also caught today several little crabs and barnacles.

I kept one specimen, to show old and young barnacles attached to the same Velella.
The sea was, this morning, covered in places with fleets of the Velella of Lamarck; also with great numbers of the species of Janthina which I described yesterday; to both of these kinds of animals large clusters of barnacles were frequently attached.

These barnacles preyed on the different gelatinous animals which were swimming about.