P. nucleus.
P. femoralis. The femoral Perna. Pl. [14], fig. 1.
Species elongated, and with appendages like ears.
P. vulsella. The tweezer Perna.
Species elongated, without earlike appendages, or having very small ones.
P. ephippium. The saddle Perna.
Species round, compressed, very pearly in the interior; very slightly, if at all, auricled; margin acute; exterior purplish brown.
3. Malleus. The Hammer. Six species.
A shell of a singular form, resembling a pickaxe, found only in the Indian and Australian Seas; there are two species, the white and the black, both of which, when in fine preservation, are highly esteemed, but the white is more rare and valuable.
Shell sub-nacreous, irregular, rugged, sub-equivalve, inequilateral, generally auricled before and prolonged behind, so as to be in form like a hammer; summit entirely anterior; between them and the inferior auricle, an oblique cut or slope for the passage of the byssus; hinge linear, elongated, without teeth; ligament simple, triangular, inserted in a conical oblique cavity, partly exterior; one rather large sub-central muscular impression.