374 



THE INVERTEBRATA 



but has lost the habit of Hving in shells and so thoroughly taken on 

 the build of the true crabs that only some asymmetry of the abdomen 

 and a few other minor points of structure betray its ancestry, even 

 the uropods being absent, 



Galathea^ the plated lobster, another of the Anomura, is lobster- 

 like but has the abdomen bent under the thorax, and the last leg 

 small and slender and folded into the gill chamber. 



Porcellana, the china crab, related to Galathea, has a form of body 

 resembling that of the true crabs, but possesses uropods. 



Fig. 279. Lithodes maia, ?, in ventral view. From the Cambridge Natural 

 History, ab.^, lateral plates of the third abdominal somite; ab.5, left lateral 

 plate of the fifth abdominal somite; mar. marginal plate; Te.6, telson and 

 sixth abdominal somite, fused; th.8, brush-like last thoracic limb. 



Ca?icer, the edible crab, is nearly related to Carcinus but more 

 heavily built, without the slight powers of swimming possessed by 

 the latter, and differing in other small points. 



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

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

 cealment. 



Gecarcinus, containing land crabs of the tropics, differs from 

 Carcinus 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. 



