These molluscs lie vertically in their deep burrows at low-water mark, the opening of the burrow having a form resembling that of a keyhole. While covered with water they occupy the upper portion of their abode, but sink to a depth of a foot or more when the tide goes out. As we walk along the water’s edge at extreme low tide we may observe jets of water that are shot into the air before us. These are produced by the sudden retreat of the ‘Razor-fish’ to the bottom of its burrow when alarmed by the approaching footsteps. Owing to this wariness on the part of the mollusc, and to the considerable depth of its burrow, specimens cannot be obtained by digging without much labour; but if a little salt or some other irritant be dropped into the hole, the animal will soon rise to eject it, and may then be shut out from the lower part of the burrow by sharply driving a spade below it. This is undoubtedly the best method of securing perfect specimens for study or preservation, but fishermen often obtain large numbers, either for food or for bait, by suddenly thrusting a long hook down into the gaping shells, and then pulling them out. This method always does injury to the soft body of the animal, and often damages the shell, but answers the fisherman’s purpose exactly. We give illustrations of two shells belonging to the typical genus (_Solen_), including one on Plate V.; also a British representative of each of two other genera of the family--_Cerati-solen_ and _Solecurtus_, the latter of which, as the name implies, contains shorter species. [Illustration: FIG. 140.--1. _Solen ensis._ 2. _Cerati-solen legumen._ 3. _Solecurtus candidus_] The next family--the _Tellinidæ_--contains a number of well-known molluscs that burrow into sand or mud, and are enclosed in shells that are often very prettily marked; and although the family includes several genera, all may be recognised by the following general features. The shell is compressed, composed of two equal valves, with little or no gape, and the ligament situated on the shortest side. The central or _cardinal_ teeth never exceed two in number in each valve, and the adductor impressions are round and polished. The mantle is quite open at the anterior end, and its margins are fringed; the foot is flattened and tongue-shaped; and the siphons, which are quite separate, are generally long and slender. In the typical genus (_Tellina_), of which we represent two very common British species, the ligament is very prominent, and the slender siphons are often much longer than the shell. The members of this group move very freely, travelling about by means of a broad, flattened foot. [Illustration: FIG. 141.--_Tellinidæ_ 1. _Psammobia ferroensis._ 2. _Donax anatinus._ 3. _Tellina crassa._ 4. _Tellina tenuis._ 5. _Donax politus_]