The Fourth Memoir, published in my Zoological Researches and Illustrations, No. III. page 69, &c., having first made known the real nature of the
Cirripedes
, the key of which remained concealed in their metamorphosis, it might have been expected that some naturalist favourably situated to investigate the oceanic tribe of these animals, would have been the first to make the same discovery in regard to these, and thereby complete their natural history. It was scarcely to be expected that the honour of this discovery also should be reserved for the author, fixed to one spot, where none of them naturally exist, and are but casually thrown upon our shores by the waves of the Atlantic, attached to pieces of wreck, or brought into port fixed to the bottoms of ships returning from distant voyages. Fortunately, however, two ships of this description came into this harbour (Cork), one from the Mediterranean, the other from North America, which, not being sheathed with copper, had their bottoms literally covered with Barnacles of the three genera of
Lepas
,
Cineras
, and
Otion
; and having persons employed expressly for the purpose, numbers of these were brought alive in sea water, amongst which were many with the ova in various stages of their progress, and some ready to hatch, which they eventually did in prodigious numbers, so as to enable him to add the proof of their being, like the
Balani, natatory
Crustacea
in their first stage
, but of a totally different facies and structure; a circumstance which determines the propriety of the separation of the
Cirripedes
into two tribes, and evinces the sagacity of Mr. MacLeay in being the first to indicate that these two tribes, the
Balani
and
Lepades
, were not so closely related as generally supposed. The larvæ of the
Balani
, described in Memoir IV. under the external appearance of the
bivalve Monoculi
(
Astracoda
), have a pair of pedunculated eyes, more numerous and more completely developed members, approximating to those of
Cyclops
, and of the perfect
Triton
; while, in the present type, or
Lepades
, the larva resembles somewhat that of the
Cyclops
, which Müller, mistaking for a perfect animal, named
Amymone
, and which can be shown to he common to a great many of the
Entomostraca
; or the resemblance is still more striking to that of the
Argulus Armiger
of Latreille, which, in fact, is but an
Amymone
furnished with a tricuspidate shield at the back.
Ultrastructure, dissolution and "pyritization" of Late Quaternary and Recent echinoderms
