Nearly all the Thalassinidea (Fig. 38) live in burrows, often of considerable depth, in sand or mud. Although now classed with the Anomura, these animals are lobster-like in form, loosely built, generally with short carapace and long, soft abdomen. They have usually very small eyes, which appear as if they were not of much use for vision; and some of the hinder pairs of legs are short, and carried folded against the sides of the body, probably for use when the animal is moving up or down in its burrow. Most of the Stomatopoda resemble the Thalassinidea in their mode of life, and show some curious similarities to them in structure, although by no means closely related. They are described as lying in wait for prey at the mouth of their burrows, darting out on passing fish or other animals, which they seize with their great saw-toothed claws, and retreating with great rapidity to the bottom of the burrow. Most of the Crustacea mentioned live below tide-marks, and at all events are rarely seen when the sand in which they burrow is left bare by the tide; but there are others, especially on tropical shores, which seem to have their chief period of activity when the sand or mud banks on which they live are exposed to the air. Chief among these amphibious forms in the warmer seas are the Crabs of the genera _Ocypode_ and _Gelasimus_ and some of their allies. [Illustration: _PLATE XV_ _Ocypode cursor._ WEST AFRICA. (REDUCED) _Gelasimus tangeri._ MALE ABOVE, FEMALE BELOW. WEST AFRICA. (REDUCED)]