(Section Streptoneura.)
Order 1.— Scutibranchia. Nerites, Top-shells, Ear-shells, Limpets. „ 2.— Pectinibranchia. Rock-snails, Whelks, Olive-shells, Harp-shells, Cones, Strombs or Wing-shells, Periwinkles, Carrier-shells, etc.
(Section Euthyneura.)
Order 1.— Opisthobranchia. Bubble-shells, Sea-hares, Umbrella-shells. „ 2.— Pulmonata. Land and freshwater Snails, False Limpets.
Class III.—Scaphopoda. Tooth-shells (Dentalium).
Class IV.—Lamellibranchia. Bivalved Molluscs.
Order 1.— Protobranchia. Nucula, etc. „ 2.— Filibranchia. Anomia, Common Mussel, Ark-shells, etc. „ 3.— Pseudolamellibranchia. Pearl-Oyster, Hammer Oyster, Wing-shells, etc. „ 4.— Eulamellibranchia. Freshwater Mussels, Cockles, Razor-shells, Ship-worms, etc. „ 5.— Septibranchia. Poromya, etc.
Class V.—Cephalopoda.
Order 1.— Tetrabranchia. Pearly Nautilus. „ 2.— Dibranchia. Octopus, or Poulp, Argonaut, Squids, and Cuttle fishes.