Elements of conchology Prepared Elements of conchology / Prepared for the use of schools and colleges elementsofconcho00rusc Year: 1844 78 PINNA.—ARCA.—PECTUNCULUS. The annual revenue from the pearl fishery of Ceylon is esti- mated at about $80,000. 18, The PiNN^ have two equal valves in form of a half-open fan, gaping and united by a ligament along one of their sides. A very large species is found in the Mediterranean, which lives half-buried in the sand, and anchored by its byssus, the fila- ments of which, being very strong, fine, and brilliant as silk, are employed by the inhabitants of
Elements of conchology Prepared Elements of conchology / Prepared for the use of schools and colleges elementsofconcho00rusc Year: 1844 78 PINNA.—ARCA.—PECTUNCULUS. The annual revenue from the pearl fishery of Ceylon is esti- mated at about $80,000. 18, The PiNN^ have two equal valves in form of a half-open fan, gaping and united by a ligament along one of their sides. A very large species is found in the Mediterranean, which lives half-buried in the sand, and anchored by its byssus, the fila- ments of which, being very strong, fine, and brilliant as silk, are employed by the inhabitants of some parts of Calabria and Sicily in the manufacture of precious stuffs. 19. The Arcje are dis- tinguished from all the preceding by their equi- valve shell. The hinge which extends along the side of the valves is studded with a great many little teeth, which fit into the intervals of those of Fig. 97.—ARCA. tj^g opposite side recipro' cally; in some, the Arca properly so called {Jig. 97), the hinge is rectilinear, and the shell is longer in a direction parallel to this junction; in others, named hinge PECTUNCULrs (fig. 98), the is curved, and the shell is lenticu lar in form. The first are met with near the shore in rocky situations, and are ordinarily covered by a hairy epidermis; the latter live in the mud. 20. Finally, the Trigoni^, most of the species of which are fossil, are remarkable for their peculiar hinge; the right valve is furnished with two projecting plates, crenulate
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