Family—LEPADIÆ

Cirripedia pedunculo flexili, musculis instmcto: Scutis musculo adductore solummodó instructis: valvis cceteris, siquæ adsunt, in annulum immohilem haud conjunctis.

Cirripedia having a peduncle, flexible, and provided with muscles. Scuta furnished only with an adductor muscle: other valves, when present, not united into an immovable ring.

Besides the brief characters here given others might have been added, drawn from the softer parts of the animals, but as this Volume treats only of Fossil species, they would have been in this place superfluous. Nor have I thought it advisable to give here any definition of the Sub-class Cirripedia, or of the Order which contains both the Lepadidae and Balanidas, that is the Pedunculated and Sessile Cirripedes; for the characters would likewise have had to be derived almost entirely from the softer parts of the animal. It may, however, be worth stating, that by following the metamorphoses of the Cirripedia, it can be clearly shown that the capitulum together with the peduncle, in the Pedunculated Cirripedes, and that the shell together with the operculum in the Sessile Cirripedes, that is the whole of what is externally visible, consists simply of the first three segments of the head. In many Crustacea the carapace, formed by the backward production of the three anterior rings of the head, covers the dorsal surface of the thorax, and in some it encloses the lirnbs and mouth.