most beautiful of our British shells.

Plate XIX.

Nassa reticulata, 3, is a favourite inhabitant of the tank; it burrows in search of food among the pebbles, elevating its siphon above the surface. Mangelia, 4-26, has a similar long siphon. The shell of Erato, 27, is wrapped in the lobes of the animal's mantle, as is also that of Cyprea, 28, the latter presenting a beautiful object.

Plate XX.

After Tornatella, 1, and Ovula, 2, 3, come Bullidæ, 4-27, including several genera differing remarkably in the shape and disposition of the lobes of their mantles, which in some instances, as in Philine, 20-25, cover the shell. The stomach of Scapander, 26, 27, is a remarkable kind of mill, composed of two bones, between which the food is ground. The shells of Aplysia, 28, and Pleurotranchus, 29, 30, are quite internal. Spirula, 31, belonging to the Cephalopodous or Cuttlefish tribe, is only introduced doubtfully, as there is no proof of the species living in our seas.

Plate XXI., XXII., XXIII., XXIV.

These are occupied by shells of Gasteropoda pulmonifera, so named because they breathe air by a pulmonary cavity, instead of water by gills. The Limnæadæ, or fresh-water Snails, contained in Plate I., live in water, but breathe by exposing the pulmonary cavity to air at the surface. Succinea, Plate XXII., 1-3, lives by the sides of streams, sometimes immersed. Conovulus, 4-7, affects brackish marshes. Our common Slugs yield, on dissection, thin shells, which are concealed beneath the mantle, Limax, 9-12. The shells of Testacellus, 13, 14, are fixed near the end of the foot, outside. The glassy shells of Vitrina, 15, 16, do not enclose the whole Slug-like animal. The other genera of Land Snails have shells large enough to receive the animal when retracted and withdrawn for repose.

BRITISH FOSSIL SHELLS.

The following living species are also found in a fossil state in drift and strata of the British Isles. They are all enumerated in Mr. Searles Wood's monograph of the Crag Mollusca.

The numbers refer to the species as figured in our Plates, Mr. Wood's nomenclature being inserted in italics when differing from ours.

Pl. I. Teredo 2. Pholas 11. Pholadidea 12. Gastrochæna 14, as dubia. Saxicava 15, 16. Venerupis 18. Mya 19, 20. Panopea 21, 21*, as Faujasii. Corbula 22, 23? Sphænia 25. Neæra 27.

Pl. II. Poromya 1. Pandora 2, as inæquivalvis, 3, as pinna. Thracia 7, 8. Solen, 13, 15. Solecurtus 18, as Mactra strigilata. Syndosmya, as Abra, 19, 22.

Pl. III. Psammobia 1, 3, 4. Tellina 5, 6, 7, 9, as ovata, 15, as Balthica, 16. Scrobicularia 18, as Trigonella plana. Donax 19, as vittatus. Mactra 20, 21, 22, as ovalis, 23, 25, 26.

Pl. IV. Lutraria 2. Tapes 7, 8. Artemis 11. Venus 12, 14, 15, 17. Astarte 18, 19, 20, 22, as borealis.

Pl. V. Cyprina 1. Circe 2. Isocardia 3. Cardium 6, 8, 9, 12, 13. Lucina 14, as Loripes, 15, as Cryptodon flexuosum, 16. Diplodonta 19. Clausina 20, as Cryptodon f.

Pl. VI. Montacuta 1, 2, 3. Kellia 5, 6. Poronia 7, as Kellia r. Cyclas 16, 18. Pisidium 23, 24, 25, 26.

Pl. VII. Unio 2, 3. Anodon 4. Modiola 6, 9, 10. Crenella 13, 14, 15, 16. Mytilus 18, 19, 20.

Pl. VIII. Nucula 1, 5. Leda 6, 7. Area 9, 10, 11, as pectunculoides. Pectunculus 13. Avicula 15. Pinna 16. Ostrea 17. Anomia 18, 19, 20, 21. Lima 22, 23, 24.

Pl. IX. Pecten 1, 2, 5, 8, 9, 10, 11, 12, 13, 14.

Pl. X. Chiton 7, as fascicularis. Patella 18. Acme 23. Propilidium, as Tectura, 24. Dentalium 26, 27. Capulus 28. Calyptræa 29.

Pl. XI. Fissurella 1, as græca. Puncturella 3. Emarginula 5, 6. Trochus 8, 10, 11, 12, as papillosus, 15, 16, 17, 19. Margarita 21. Adeorbis 25. Scissurella 26.

Pl. XII. Paludina 9. Valvata 10. Littorina 14. Lacuna 27.

Pl. XIII. Rissoa 3*, as Paludestrina subumbilicata, 7, 11?, 13?, 15, 23, 27.

Pl. XIV. Rissoa 2, 9, as Chemnitzia. Aclis 24, as Alvania ascaris, 25, as Chemnitzia n.

Pl. XV. Turritella 2. Aporrhais 4. Cæcum 6, 7. Cerithium 9, 10. Cerithiopsis, as Cerithium, 11. Scalaria 17, 19, 20. Eulima 22, 25.