THE PORCELAIN CRABS 171 



appendages to the fourth, to the fifth, and sometimes to the 

 third segment. 



Notwithstanding the brnchyuran characteristics this 

 legion is found to be in. close affinity with the next, the 

 Galatheinea. Here it is supposed that the pleon has 

 become reduced in size and has lost its importance as an 

 organ of locomotion, owing to the special habits which 

 the animals have adopted. They are found under stones 

 between tide-marks and in shallow water among stones, 

 sponges, and corals. One species has been taken at a 

 depth of 390 fathoms. There is but one family. 



Family Porcellanidce. 



The characters of the single family are those of 

 the legion. Eleven genera are assigned to it, most of 

 which were instituted by Stimpson in 1858, and some on 

 very slender distinctions. Only one belongs to British 

 waters. 



Porcellana, Lamarck, 1801, has the 'front' dentate, 

 the first joint of the second antennas much produced, fully 

 reaching the margin of the carapace. The chelipeds 

 have a projecting lobe near the base of the inner margin 

 of the fifth joint, the terminal joint often contorted. The 

 walking-legs have the terminal joint short and robust, 

 ending in a single claw. To this genus belong the only 

 British species of the family, Porcellana platycheles (Pen- 

 nant) and Porcellana longicornis (Linn.), both of which 

 are common under stones, along which they slidder with 

 some rapidity. They will sometimes flatten themselves 

 against the upturned stone, remaining quiet and evidently 

 trying to look as if they were not there. Quite after the 

 fashion of their kindred, the Galatheidas, they will lift up 

 their claws to resist attack, but their flattened habit of 

 body makes this posture of defence in their case ridicu- 

 lously ineffective. If one of the threatening claws be 

 seized, they pretty readily relinquish it and skurry away. 

 To understand the likeness between these crustaceans and 

 the Galatheidge it is necessary to flatten out the pleon of 



