perna and pernocchia meant a shellfish which yielded "nacre" or mother-of-pearl.
The borings of marine shellfish visible in these columns between II and 19 ft.
This was properly the name of the shellfish (Purpura, Murex) which yielded the famous Tyrian dye, the particular mark of the dress of emperors, kings, chief magistrates and other dignitaries, whence "the purple" still signifies the rank of emperors or kings.
The western and larger species gathers its food, consisting chiefly of sea-weeds and shellfish, on rocks at low water; but it is also known to eat birds' eggs.
perna, a ham-shaped shellfish, but this is due to Florio, who by a mistake glosses parnocchie, prawne-fishes or shrimps.