ORDER III. The PESTACEA, have the same characters with those of Order II. but are covered with a shell.—This order includes 36 genera, viz. Cliton, Lepas, Pholas, Mya, Solen, Tellina, Cardium, Mactra, Dogas, Venus, Spondylus, Chama, Arca, Ostraca, Anomia, Mytilus, Pinna, Argonauta, Nautilus, Conus, Cypræa, Bulla, Voluta, Buccinum, Strombus, Murex, Trochus, Turbo, Helix, Nerita, Haliotis, Patella, Dentalium, Serpula, Tereedo, Sabella.