VI FAMILIES OF PAGURIDAE BRACHYURA l8l 



mated at the base ; the chelipedes are equal or subequal, or the 

 left is much larger. Chiefly in the warm and tropical seas, but 

 Clihanarius and Diogenes also in the Mediterranean. 



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 (Pig. 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. Hwpalogaster and Bermaturus 

 in the North Pacific littoral. 



Sub-Fam. 2. Lithodinae. — Abdomen fully calcified, with a 

 complicated arrangement of plates. Litliodes (Pig. 121) practi- 

 cally universal distribution, littoral and deep sea. AcantJiolithus, 

 deep littoral of Japan ; Faralomis, west coast of America. This 

 last genus should probably be placed in a separate family. 



Sub-Order 3. Brachyura.^ 



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. 



The larva hatches out as a Zoaea ^ (Fig. 124, A) very similar 

 to that of the Anomura ; it is furnished with an anterior and 

 ■posterior spine on the carapace. It is characteristic of the 

 Brachyuran Zoaea that the third maxillipede is fashioned from 

 the beginning in its definitive expanded form, and is never a 

 biramous swimming organ as in the Anomura. The only excep- 



^ For general literature consult Ortmann in Bronn's Tier-Eeich, v . 2, 1901, p. 778. 

 See also Reports of Challenger, Valdivia, and Talisman Exiicditions, etc. 

 ^ Gurney, Quart. J. Micr. Set. xlvi., 1902, p. 461. 



