e on each side.

Extremely common; attached to ships' bottoms, from all parts of
the world; on floating timber; associated with _L. anatifera_
and _L. anserifera_. Mediterranean. Attached to turtles, in the
Atlantic, lat. 30 deg. north. West Indies. Falkland Islands. "South
Seas," collected by A. Menzies. Port Stephen, Australia.

_General Appearance._--Capitulum laterally flat; length varies in
proportion to the breadth; valves white, somewhat translucent,
moderately thick, very smooth, but with faint traces of radiating lines;
in some varieties, surface rather irregular along the zones of growth.
_Scuta_ without any internal teeth, and with scarcely any trace of the
internal basal rim; upper angle little acuminated; the occludent margins
of the two scuta stand rather separate from each other, showing a wide
space of corium between them: these margins are arched and protuberant,
but with the lower part a little hollowed out; basal margin a little
curved. In one specimen alone, I saw a trace of a diagonal line of
square coloured marks, like those common in _L. anatifera_. _Terga_
rather broad, with the basal angle not much acuminated. The degree of
prominence and outline of the double occludent margin varies very much.
_Carina_, separated by a rather wide space from the scuta and terga; of
very varying shape, the upper part not much acuminated, generally very
flat, sometimes exteriorly marked by a central depressed line; never
barbed; occasionally, (in a specimen from Australia,) middle part so
wide as almost to become spoon-shaped; on the other hand occasionally of
nearly the same width throughout; somewhat constricted above the fork.
Fork deeply embedded as usual; situated, in fresh specimens, a little
way beneath the basal margins of the scuta, instead of touching them, as
in the other species; forks of varying width, not so abruptly inflected
as in many species; sometimes much narrower than the upper widest part
of the valve, sometimes nearly twice as wide; prongs of fork not very
sharp, diverging at about a right angle, with the rim between them
reflexed. The apex of the carina extends up between the terga for barely
half their length, instead of up fully three fourths of their length,
as in _L. anatifera_.

The chitine membrane at the base of the capitulum, especially at the
anterior and posterior ends, is covered with beautiful, little,
embedded, yellowish beads, about 3/2000th of an inch in