DECAPODA 417 



resembling that of the true crabs, but possesses uropods. Fig. 266 A 

 shows its remarkable zoaea. 



Cancer, the edible crab, is a member of the Brachyura, nearly re- 

 lated to Carcinus but more heavily built, without the slight powers of 

 swimming possessed by the latter, and differing in other small points. 



Gecarcinus, containing land crabs of the tropics, differs from Car- 

 cinus and Cancer in the shape of the third maxillipeds, which gape, 

 the sternal position of the male opening, and the highly vascular lining 

 of its swollen gill chambers. Its Zoaeae are marine. 



Maia, the spiny spider crab, is narrow in front, with bifid rostrum 

 and feeble chelae, and a habit of decking itself with seaweed for 

 concealment. 



