Established by Daudin; classed by Linnæus with the Solen, but Lamarck is
of opinion that it more nearly approximates the Cardita.
Shell thin, sub-rhomboidal, equivalve, very inequilateral, gaping at its
inferior margin and posterior extremity; the summit very anterior and
recurved in front; dorsal hinge formed by a single tooth on one valve
corresponding to a semicircular slope on the opposite valve, or by a
small tooth with a cardinal cavity in each valve; ligament probably
exterior and dorsal; muscular impressions unknown.
Hiatella Arctica.
Hiatella biaperta.
_H. Arctica._ The Arctic Hiatella.
Shell small, transversely oblong; apices truncated, with two divergent
spring ridges; a small tooth on each valve; cream colour, with
decussated striæ; inside pearly.
_H. biaperta._ The double-clefted Hiatella. Pl. 10, fig. 4.
Species that has only a single tooth on one valve; yellowish white.