I 76 CRUSTACEA—EUCARIDA—DECAPODA CHAP. 
segment; following these there are four large plates (1-4) 
representing the terga of the first four abdominal segments ; the 
fifth, sixth, and the telson are, as has been stated, carried on the 
under side of the abdo- 
men, but they are re- 
presented diagrammati- 
eally (5, 6, 7) im the 
dorsal view. — Besides 
the large terga, there 
are a number of small 
plates laterally, usually 
two to each segment, 
but they show a ten- 
dency to subdivide and 
increase in the largest 
specimens. This condi- 
F1G. 120.—Dorsal view of abdomen, A, of Cenobita, tion of affairs is very 
spss B, of Birgus latro. T, Telson; 1-6, 1st-6th different to that in the 
abdominal segments. 
naked fleshy abdomen 
of an ordinary Pagurid, but it can easily be deduced from 
that of the genus Cenobita, ordinary Hermit-crabs found in the 
Indo-Pacific Oceans, from which the Robber-crab has evidently 
descended. In Cenobita (Fig. 120, A) we see the same system 
of plates upon the dorsal surface of the abdomen, but they are 
much smaller, and the lateral plates are not so numerous ; 
indeed, the greater part of the abdomen remains fleshy and 
unealcified. The under surface of the abdomen shows the same 
rugosity as is found in Sirgus, and from a number of other 
anatomical characters it is evident that the Robber-crab is a 
highly modified Cenobita that has deserted its shell and developed 
a symmetrical abdomen protected by expanded and hardened 
plates which represent those found in a reduced condition in 
Cenobita. The species of Cenobita although they inhabit shells 
and have normal branchiae, live on the shore, and have not been 
seen to descend actually into the sea. 
The Lithodidae, which are found in temperate seas, especially 
on the Northern Pacific coasts (though Lithodes maia occurs in 
the North Sea, and certain species inhabit deep water in the 
Indian Ocean), have a deceptively Brachyuran appearance, the 
thorax being much shortened and the abdomen being much 
