AMPHINEUEA. 



7 



The following Table shows the systematic arrangement of the Syste 



Mollusca adopted in the Shell Gallery : — • 



Class I. — Amphineura. 



Order 1. — Polyplacopliora. Chitons. 



„ 2. — Aplacoplioia. Neomenia, Chietodernia, etc. 



Class II. — Gastropoda. 



(Section Streptoneura.) 

 " ^ 5 ' 



Order 1. — Scutibranchia. Nerites, Top-shells, J^ar-sheljs, Limpets. . 



„ 2. — Pectinibranchia?^ Rock-snails, Whelks, Olive-shells, Harp-shells, 



Cones, Strombs or Wing-shells, Periwinkles, Carrier-shells, etc. 



. ' "^ /! 



(Section Euthyneura.) 



Order 1. — Opisthobraucliia. Bubble-shells, Sea-hares, Umbrella-shells. 

 „ 2. — Pulraonata. Land and freshwater Snails, False Limpets. 



Class III. — Scaphopoda. Tooth-shells {DentaUum). 



Class IV. — Pelecypoda. Bivalved Molluscs. 

 Order 1 — Protobranchia. Nucida, etc. 



„ 2. — Filibranchia. Anomia, Common Mussel, Ark-shells, etc. 



„ 3. — Eulamellibranchia. Freshwater Mussels, Cockles, Razor-shells, 



Oysters, Ship-worms, etc. 

 „ 4. — Septibranchia. Poromya, etc. 



Class V. — Cephalopoda. 



Order 1. — Tetrabranchia. Pearly Nautilus. 



„ 2. — Dibranchia. Octopus, or Poulp, Argonaut, Squids, and Cuttle- 

 fishes. 



matic 

 arrange- 

 ment. 



Class I.— AMPHINEURA. 



The Molluscs of this class are characterized by bilateral symmetry. Oases 1-3. 

 The head and anus are situated at the opposite extremities of the 

 elongated body, the gills, genital ducts and circulatory organs being 

 paired and similar on both sides. The first order belonging to this 

 division, the Polyplacophora, includes the " Coat-of-mail shells," or 

 " Sea-woodlice " {Ghitonidce,). They have their back protected with 

 eight shelly plates which overlap one another like tiles, and, like 

 woodlice, have the power of rolling themselves into a ball. These 

 plates are imbedded at the sides into the fleshy mantle, beneath 

 which, on each side of the foot, are arranged the gills. A Chiton 

 differs in many respects from other Mollusca. It has a shell like an 

 Isopod' Crustacean, a heart down the back like a sea-worm, sym- 

 metrical organs of reproduction on each side like the bivalves, a 

 head and crawling foot like a true Limpet, and a posterior anal 



