190 



DECAPOD CR USTA CEA. PART m. 



tion the highest of the Crustacea. Though apparently 

 without a tail, they really have one, as their name 

 implies ; but it is short, rudimentary, and folded under 

 the posterior end of the carapace. The genera and 

 species are exceedingly numerous, many swim and 

 inhabit the deep oceans, others live on the coasts but 

 never leave the water ; a numerous tribe live as much 

 in the air as in the water, hiding themselves under 

 stones and sea-weeds on the rocky coasts, while some 

 dig holes for themselves in the sand, and the land crabs 

 only come to the sea or to fresh-water lakes to spawn. 

 The Brachyura have two claws, and are divided into 

 the two chief families of walking and swimming crabs, 

 according as their posterior pairs of legs end in a sharp 

 horny nail, or a ciliated lamellar joint. 



The great shell or carapace which covers the body 

 varies in form with the genera ; it may be square, oval, or 

 circular, longer than it is broad, or broader than it is 

 long ; it may be straight or beaked between the eyes ; but 

 its lateral edges always extend over the haunches of the 

 feet. In the Cancri, or walking crabs, of which there 

 are eighteen genera and many species, the carapace is 

 generally much broader than it is long, and broader 

 before than behind. 



The carapace, or shell, of the common crab is too well 

 known to require a particular description. The deep 

 lines which indent it correspond with the limits of the 

 internal organs; the parts between the lines often 

 bulge very much above the parts occupied by the 

 stomach, heart, gill chamber, &c., but in the flat crabs 

 these divisions are not so evident. 



The compound eyes, which in all the crabs have 

 hexagonal facettes, are on short jointed stems placed in 

 deep and nearly circular orbits like cups, so that the 

 stems are scarcely visible. These orbits, whose edges are 

 sometimes smooth and sometimes notched, are so con- 



