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 The other genera of Land Snails have shells large enough to receive the animal when retracted and withdrawn for repose.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.