CHAPTEE X. 

 THE DECAPOD CRUSTACEA THE TRUE CRABS. 



Common spider-crabs Their coating of weed The general characters 

 The edible crab Its distribution and habits The shore crab 

 Different kinds of swimming crabs The pea-crab Movements of 

 the Decapod Crustacea Process of moulting Development of 

 Crustacea. 



IN this chapter we have to consider the true crabs, one of 

 the most interesting groups of the Crustacea, including 

 forms which are essentially littoral in habit. We have 

 already seen that the porcelain-crabs, the stone-crab, and 

 the masked crab, show striking external resemblances to the 

 true crabs, such as the spider-crabs, the shore crab, and the 

 edible crab, so that a little care is necessary in defining the 

 Brachyura, or short-tailed true crabs, in the narrow sense. 

 That the carapace is usually broad in proportion to its 

 length, and the tail small without tail fan, and reflexed 

 beneath the body in all crabs, it is hardly necessary to 

 repeat. More subtle points are the fact that eyes, an- 

 tennules, and antennae, are placed in complete sockets, that 

 the third pair of maxillipedes form flattened plates (opercula) 

 instead of being leg-like, and that the whip (flagellum) of 

 the antennae is always short. Lest it should seem, however, 

 that this distinction has been made too sharp, it should be 

 carefully noted that in the curious rounded crab Atelecydus, 

 mentioned in the last chapter, the maxillipedes are com- 

 pletely flattened, and meet in the middle as they do in the 

 true crabs. Such facts make the classification of the 

 crabs as difficult as it is interesting, but as we are con- 

 cerned only with British forms, it is sufficient to regard 



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