es, or rather to different specimens, for some of them
are undistinguishable. A specimen from the Sandwich Islands, sent by Mr.
Conrad to Mr. Cuming, is marked _A. engonata_.

In looking over a large collection of specimens in a museum, the most
distinctive characters appear at first to be the colours, the dentation
or barbed condition of the carina, the row of square marks on the scuta
and terga, and the more or less produced form of the whole capitulum:
all these characters are absolutely worthless as distinctive characters,
and blend into each other. In a fresh condition, the colours of this
species, and of _L. anserifera_ and _L. Hillii_ are surprisingly alike,
though in _L. anatifera_ alone, the uppermost part of the peduncle is
dark. As far as I have seen, the smoothness of the valves, together with
the presence of a tooth beneath the umbo, on the right-hand scutum, and
its entire absence on the left side, (in other species it is smaller on
this, than on the right-hand side,) is an unfailing diagnostic mark. I
believe this species is always attached to floating objects, though
there are some very young specimens in the British Museum, collected by
Sir G. Grey, adhering to sandstone, but this may have been buoyed up by
some large sea-weed. Mr. Peach has given me the particulars of two
instances, in which, after gales of wind, this species, of nearly full
size, adhering to _apparently_ freshly broken-off Laminariae, has been
cast upon the coast of England and Scotland.

2. LEPAS HILLII. (Pl. I, fig. 2).

ANATIFA vel PENTALASMIS LAEVIS (!) plerumque auctorum.

PENTALASMIS HILLII (!). _Leach._ Tuckey's Congo Expedit. p. 413,
1818.

---- CHELONIAE (!) Ib. Ib.

ANATIFA TRICOLOR (?). _Quoy_ et _Gaimard_. Ann. des Sc. Nat., 1st
series, tom. x, 1827, Pl. vii, fig. 7, et Voyage de
l'Astrolabe, Pl. xciii, fig. 4.

---- SUBSTRIATA (!). _Conrad._ Journal Acad. Nat. Sc.,
Philadelphia, vol. vii, 1837, p. 262, Pl. xx, fig. 14.

_L. valvis laevibus; scutorum dentibus internis umbonalibus nullis;
carina a caeteris valvis, furca etiam a scutorum basali margine, paululum
distante; pedunculi parte superiore aut pallida aut aurantiaca._

Valves smooth; scuta destitute of internal umbonal teeth; carina
standing a little separate from the other valves, with the fork not
close to the basal margin of the scuta; uppermost part of peduncle
either pale or orange-coloured.

Filaments thre