e 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
occluden