=Fam. 3. Cenobitidae.=—The abdomen is as in Paguridae. The antennal scale is reduced, the flagella of the first antennae end bluntly. The members of this family are characteristic of tropical beaches, where they live on the land. _Cenobita_, with about six species, in the West Indies and Indo-Pacific, living in Mollusc shells; _Birgus_ (Fig. 119) on Indo-Pacific coral islands. =Fam. 4. Lithodidae.=—The abdomen is bent under the thorax, and the body is crab-like and calcified. The rostrum is spiniform, and the sixth abdominal appendages are lost. =Sub-Fam. 1. Hapalogasterinae.=—Abdomen not fully calcified, and without complicated plates. _Hapalogaster_ and _Dermaturus_ in the North Pacific littoral. =Sub-Fam. 2. Lithodinae.=—Abdomen fully calcified, with a complicated arrangement of plates. _Lithodes_ (Fig. 121) practically universal distribution, littoral and deep sea. _Acantholithus_, deep littoral of Japan; _Paralomis_, west coast of America. This last genus should probably be placed in a separate family. =Sub-Order 3. Brachyura.=[147] The abdomen is much reduced, especially in the male, and is carried completely flexed on to the ventral face of the thorax so as to be invisible from the dorsal surface. The pleopods in the male are only present on the two anterior segments, and are highly modified as copulatory organs; the pleopods in the female are four in number and are used simply for carrying the eggs; the pleopods of the sixth pair are always absent in both sexes. The first antennae and the stalked eyes can be retracted into special pits excavated in the carapace. [Illustration: FIG. 124.—=A=, Zoaea, × 24, and =B=, Metazoaea, × 13, of _Corystes cassivelaunus_. _Ab_, 3rd abdominal segment; _An_, 1st antenna; _E_, eye; _G_, gills; _M_, 1st maxillipede; _T.8_, last thoracic appendage. (After Gurney.) ] [Illustration: FIG. 125.—Later stage (Megalopa) in the development of _Corystes cassivelaunus_, × 10. _A_, Antenna; _Ab_, 3rd abdominal segment; _C_, great chela; _T.8_, last thoracic appendage. (After Gurney.) ]