Fig. 15.—Shells of a Barnacle, Balanus hameri, found in European and North American Seas, natural size.
Fig. 16.—Hermit Crabs. A, Aniculus typicus, from the Indo-Pacific Seas, one-half of the natural size. B, Caternus tibicen, from the Indo Pacific Seas, slightly enlarged.
The true Crabs are called Brachyura, or Short-tails; for obvious reasons, the tail of a crab being very curiously modified and tucked in under the carapace or "shell." A form exceptional in the fact that frequents the land is the Land-Crab of the West Indies ([Fig. 17]). Another land crustacean, Birgus latro, the Robber Crab, belongs to the previous group.
Fig. 17.—Land Crab, Gecarcinus ruricola, from the West Indies, one-half of the natural size.