BIVALVE MOLLUSCA. 371 
nine pennyweights, all of perfect form and of the finest water. The 
Romans were passionately fond of pearls, and they have transmitted 
their taste to the Eastern nations, who attach notions of great 
grandeur and wealth to the possessor of large and brilliant pearls. 
The genus Pinna, was so called by Linnzus, from one of the species 
which was so designated from the resemblance of its byssus to the 
aigrette or plumelet which the Roman soldiers attached to the helmet. 
French naturalists name them sambonneaux, from their singular resem- 
Fig. 165.—- Pinna rudis (Linnzus). Fig. 166,—Pinna nigrina (Lamarck). 
blance to a dried ham (Figs. 165 and 166), their brown, smoky colour 
not a little aiding the resemblance. The shell is fibrous, horny, very 
thin and fragile, compressed, regular, and equivalve, triangularly 
pointed in front, round or truncated behind. The hinge is linear, 
straight, and without teeth; the ligament, in great part internal, 
occupies more than half the anterior portion of the dorsal edge of the 
shell, forming a straight elongated fossette. 
The animal is thick, elongated, with mantle open behind, presenting 
a conical furrowed foot, bearing a considerable byssus. 
The species of the genus Pinna are found in almost every sea, and 
at various depths; they are constantly attached by their byssus, and 
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