As one observes the nature and movements of these interesting little crabs one cannot fail to see how beautifully their form and structure are adapted to their habits. They are peculiarly constructed for abode in narrow chinks and crannies, and for feeding on the small forms of life that inhabit such sheltered places. Their legs move in the plane of their flattened bodies, and as they glide among the confervæ and other low forms of life that encrust the stones of the beach they feel their way by, and are possibly also guided by the sense of smell located in, their long outer antennæ, while the close fringes of their claws and foot-jaws form admirable sweep-nets by means of which the little animals that form their food are swept towards the mouth. We have other species of stone crabs, one or two of which resemble the last species, and belong to the same genus, but the others are very different in general appearance. The Northern Stone Crab (_Lithodes_), found principally on and off the coasts of Scotland and Ireland, has a spiny covering with a long beak. Another species--_Dromia vulgaris_--is somewhat similar in habit, though it can hardly be termed a stone crab, since it inhabits deep water, and apparently lives among the sponges, sea firs, and weeds that cover the bottom. [Illustration: FIG. 212.--_Dromia vulgaris_] [Illustration: FIG. 213.--THE HERMIT CRAB IN A WHELK SHELL] The remainder of the Peculiar-tailed Decapods belong to the Soldier or Hermit Crabs, and constitute the genus _Pagurus_. Every one who has searched a few rock pools will have seen the familiar Hermits, and will probably have been interested in their varied antics. First you observe the shell of a mollusc--a Trochus, Periwinkle, or a Whelk--travelling at an abnormal rate for a member of its class. You approach closely to make an inquiry into the matter, when the motion suddenly ceases, and the shell instantly drops into position with its mouth close to the surface below. If left undisturbed for only a short time, the rapid and somewhat jerky motion is resumed, only to cease as suddenly as before as soon as the inhabitant is again threatened. On examining the shell we find that it is the home of a species of crab, and that the animal within it is completely hidden with the exception of its head, stalked eyes and long, slender antennæ, one very large claw, and a few walking legs.