THE ORDER OF DECAPODA 255 



which these legs are not only chelate, but are 

 monstrously enlarged ; and (3) the Caridea (shrimps), 

 which never have these legs (third pair) chelate. 



The Anomala, in whom the antennal scale, if 

 present at all, is a mere spine, are more highly 

 organised than the Macrura. Some of them have an 

 almost misleading resemblance to crabs, but even the 

 most crab-like of them (such as Lithodes and Para- 

 lomis) are slightly lop-sided, and never have the 

 partition or septum between the first pair of antennae, 

 which is diagnostic of the Brachyura. Others of 

 them have a strong resemblance to certain kinds of 

 lobsters, but these can always be distinguished, even 

 from those Macrura which have no antennal scale, by 

 the facts that the abdomen is folded beneath the 

 cephalothorax, and the last pair of thoracic legs are 

 rudimentary. We recognise three brigades of the 

 Anomala, namely the aberrant Hippides, or mole- 

 crabs, which burrow in the sand ; the Pagurides, or 

 true hermit-crabs, most of which, though by no means 

 all, live in a cast-off mollusk shell ; and the Gala- 

 theides, which look something like small lobsters, but 

 are sedentary, and so have the abdomen permanently 

 bent. 



The Brachyura, or crabs, are the highest of all the 

 Crustacea, as is shown by the concentration of the 

 segments and consequent centralisation of the nervous 

 system, and by the more perfect specialisation of the 



