THE MARINE AQUARIUM. 125 



and though a creeping crab, it seems to thrive. The 

 difference in form between the creeping and swimming 

 crabs consists in the former having all their legs fashioned 

 iu a similar manner, while the latter have the hinder- 

 most pair of legs flattened into a pair of oars, by which 

 they "skull" themselves along, and it is by such means 

 of progression they move through the water, the legs 

 that are to go forwards being drawn up nuder the body, 

 whilst the others are extended behind as the oar-shaped 

 lco- propels the body onwards. It has been asserted, that 

 all crabs move sideways ; this is true of many, but the 

 "hermit" oftener moves backwards, pushing his cumbersome 

 shell on behind him. The Gclasinms has been also called 

 the soldier-crab from its fighting propensities, elevating its 

 largest claw on the least alarm as it moves over the 

 wet sand in which it burrows and seems most to live. 

 When it is introduced into the water, it attempts to get 

 out as soon as possible ; and from this fact it might 

 seem that it could not become an inhabitant of the 

 Aquarium; but I have one that has been iu my tank 

 for the last four months and does not appear now to 

 be dissatisfied with its place of residence. 



The common Edible Crab (Lupa dicanlha — Plate VII. 

 Fig. 2) is an excellent inhabitant of an Aquarium and belongs 

 to the class of swimming crabs. It is found in large quan- 

 tities on the American coast from Florida to Cape Cod, 

 Massachusetts, but when over an inch or two in length, 

 it is too large for our purpose. The process of slough- 

 iiif or casting the shell occurs aunually and is of short 

 duration, scarcely ever exceeding the period of forty-eight 



