This genus is the same as constituted by Linnæus; the shell is marine,
generally very brittle and fragile, in form resembling an acute angled
triangle; usually covered with longitudinal ribs and elevated transverse
striæ; generally horn coloured.
This genus is remarkable for the production of an abundant byssus of a
fine brown silky texture, which the Italians frequently fabricate into
articles of dress, equal in appearance to the finest silk.
The Pinnæ often grow to a large size; they are sometimes found standing
erect in the smooth-water bays, with the base of the shell uppermost,
but generally affixed by the byssus to rocks and other sub-marine
bodies. The filaments that compose the byssus are so tough and strong
that the shells are not easily detached.
Shell fibrous, fragile, regular, equivalve, longitudinal, triangular,
base gaping and as if truncated; summit pointed and straight; hinge
dorsal, longitudinal, linear, and without teeth; marginal ligament
occupying almost the whole of the dorsal edge of the shell; one very
broad muscular impression behind a trace of the anterior in the summit.
Pinna rudis.
P. flabellum.
P. seminuda.
P. angustina.
P. nobilis.
P. squamosa.
P. marginata.
P. muricata.
P. pectinata.
P. saccata.
P. varicosa.
P. dolabrata.
P. ingens.
P. vexillum.
P. nigrina.
_P. squamosa._ The scaly Pinna.
Species very close and rounded at the posterior extremity; valves
convex, covered with vaulted imbricated scales.
_P. flabellum._ The fan Pinna. Pl. 13, fig. 2.
Species gaping at the posterior extremity, which is as if truncated;
valves rather rounded at the upper end, and in the shape of an expanded
fan; light fawn colour.
_P. pectinata._ The pectinated Pinna. Pl. 13, fig. 1.
Thin, pellucid; longitudinally ribbed and spinous for half its width,
obliquely striated transversely on the other half.
FAMILY XVII.
MALLEACEA. Five genera.