The part supported by the peduncle, and which is generally, though not always, protected by valves, I have designated the Capitulum.
The title of Peduncle, which is either naked or squamiferous, requires no explanation; the scales on it, and the lower valves of the capitulum, are arranged in whorls, which, in the Latin specific descriptions, I have called by the botanical term of verticillus.
I have applied the term Scutum to the most important and persistent of the valves, and which can generally be recognised by the hollow giving attachment to the adductor scutorum muscle, from the resemblance which the two valves taken together bear to a shield, and from their office of protecting the front side of the body. From the protection afforded by the two Terga to the dorso-lateral surface of the animal, these valves have been thus called. The term Carina[2] is a mere translation of the name already used by some authors, of Keel-Valve.
[2] In the Carina of Fossil Species of Scalpellum, I have found it necessary to distinguish different parts, viz., A, the tectum, of which half is seen; B, the parietes; and C, the intra-parietes.
The Rostrum has been so called from its relative position to the carina or keel. There is often a Sub-carina and a Sub-rostrum.
The remaining valves, when present, have been called Latera; there is always one large upper one inserted between the lower halves of the scuta and terga, and this I have named the Upper Latus or Latera; the other latera in Pollicipes are numerous, and require no special names; in Scalpellum, where there are at most only three pair beneath the Upper Latera, it is convenient to speak of them (vide [Woodcut, I,]) as the Carinal, Infra-median, and Rostral Latera.
As each valve often requires (especially amongst the fossil species) a distinct description, I have found it indispensable to give names to each margin. These have mostly been taken from the name of the adjoining valve, (see [fig. I.]) In Lepas, Pollicipes, &c., the margin of the scutum adjoining the tergum and upper latus, is not divided ([fig. II]) into two distinct lines, as it is in Scalpellum, and is therefore called the Tergo-lateral margin. In Scalpellum ([fig. I]) these two margins are separately named Tergal and Lateral. The angle formed by the meeting of the basal and lateral or tergo-lateral margins, I call the Baso-lateral angle; that formed by the basal and occludent margins, I call, from its closeness to the Rostrum, the Rostral angle. In Pollicipes the carinal margin of the tergum can be divided into an upper and lower carinal margin; of this there is only a trace ([fig. I]) in Scalpellum.
That margin in the scuta and terga which opens and shuts for the exsertion and retraction of the cirri, I have called the Occludent margin. In the terga of Lepas ([fig. III]) and some other genera, the occludent margin is highly protuberant and arched, or even formed of two distinct sides.
Occasionally, I have referred to what I have called the primordial valves: these are not calcified; they are formed at the first exuviation, when the larval integuments are shed: in mature Cirripedes they are always seated, when not worn away, on the umbones of the valves.
The membrane connecting the valves, and forming the peduncle, and sometimes in a harder condition replacing the valves, I have often found it convenient to designate by its proper chemical name of Chitine, instead of by horny, or other such equivalents. When this membrane at any articulation sends in rigid projections or crests, for the attachment of muscles or any other purpose, I call them, after Audouin, apodemes. For the underlying true skin, I use the term corium.