labelled _A. striata_, which is properly a synonym of _L.
anserifera_.

_L. valvis tenuibus, crasse sulcatis, saepe pectinatis; scutorum crista
prominente ab umbone ad apicem juxta marginem occludentem pertinente:
furcae carinalis cruribus inter angulos 135 deg. et 180 deg.
divergentibus._

Valves thin, coarsely furrowed, often pectinated. Scuta with a prominent
ridge extending, from the umbo to the apex, close to the occludent
margin; fork of the carina with the prongs diverging at an angle of from
135 deg. to 180 deg.

Filaments absent, or only one on each side.

Var. (Pl. I, fig. 3 _a_), upper part of the terga (bounded by the two
occludent margins) produced and sharp; surface of all the valves often
coarsely pectinated, and with the carina barbed.

Atlantic Ocean, from the North of Ireland to off Cape Horn;
common, under the tropics; Mediterranean: attached to wood,
cork, charcoal, sea-weed, a reed-like leaf, spirulae, cuttle-fish
bones, to a bottle together with _L. anatifera_; to a ship's
bottom, Belfast, (W. Thompson.) Often associated with _L.
fascicularis_. Montagu states ('Test. Brit.,' p. 18) that this
species is sometimes attached to the fixed _Gorgonia flabellum_.

_General Appearance._--The capitulum varies considerably in length
compared to its breadth, caused chiefly by the greater or less
production of the occludent portion of the terga; valves thin, brittle;
the furrowed surface varies much in character, narrow and broad ridges
often alternating; frequently each ridge (but more especially the ridge
running from the umbo to the apex of each scutum, and sometimes that
alone,) is covered with prominent, curled, flat, calcareous spines,
giving the shell an appearance like that of many mollusca. Other
specimens show no trace of these calcified projections. From the
thinness of the valves and the depth of the furrows, the margins of the
valves are sinuous. _Scuta:_ the ridge running from the umbo to the apex
is unusually prominent and curved; it runs very close to the occludent
margin, so that, differently from in all the other species, only a very
narrow space is left between this margin and the ridge. Internal teeth,
under the umbones, either sharp and prominent, or mere knobs; sometimes
that on the right side is much larger than that on the left; sometimes
they are nearly equal; sometimes that on the left is scarcely
distinguishable. Internal basal rim absent, or bar