Pvn H,i I'UitlS

PSAMMOBIA. 399
of growth are conspicuous ; the whole surface is marked by
slight and irregular longitudinal or radiating lines, as well as
by close-set microscopical striae in the same direction, but
these stria? are generally effaced ; in young shells the posterior
slope is sculptured by radiating ribs as in P. Ferroensis, but
much less : distinctly colour beneath the epidermis yellowish-
white, variegated by bright rays of a purplish-brown
or lilac
of different widths ; whether the rays are present or not, the
shell is frequently marbled, speckled, or spotted with white, and
lineated with short dusky streaks ; now and then specimens
are found having the umbones of a uniform purple hue : epidermis
rather thick and persistent, light yellowish-brown in the
young, and of a deeper or olive-brown in the adult : margins
not much rounded in front, obliquely curved towards the an-
terior side, where they are semioval and wedge-shaped, slightly
indented or flexuous on the ventral side of the lower or posterior
angle, abruptly and somewhat obliquely truncate but not
sharply angular on the last-mentioned side, which is indistinctly
denned by an obscure ridge extending from the beak to
or but little
the lower angle dorsal ; margin nearly straight
inclined, and ending in an obtuse angle which forms the upper
side of the posterior : margin beaks as in the last : species
ligament short, extremely prominent, annular and of a closely
fibrous texture, funnel-shaped, with the smaller end proceed-
the large
ing from between the beaks and widening outwards ;
end is closed and held down to the dorsal edge by a membrano
as extension, which in the young is of a yellowish colour,
the body of the separated
ligament being horncolour; the valves are
in that part as in the other species : hinge-line ob-
tusely angular or gently curved : hinge-plate rather thick,
broader on the posterior side, abruptly truncate at the outer
end of the ligament : teeth as in P. Ferroensis : inside thick-
ened, porcellanous, highly polished and slightly iridescent, yellow
or lemoncolour tinged with purple near the beak, sometimes
of a uniform lilac, marked with faint longitudinal striae
towards the front margins, and microscopically wrinkled like
shagreen : pallial and muscular scars as in the other species.
L. 1-25. B. 2-25.
Yar. 1. lactea. Shell milk-white ; all the teeth more erect
and recurved, and the smallest in the left valve triangular and
pointed instead of laminar or ridge-like.
\ r ar. 2. livida. Shell more oval, or longer in proportion to
its breadth, of a uniform fawncolour, but shaded, and marked