CHAPTEE IX. 



THE DECAPOD CRUSTACEA : LOBSTERS, CRAYFISH, 

 AND THEIR ALLIES. 



The common lobster and the Norway lobster Their distribution and 

 characters Structure and habits of the spiny lobster Habits of 

 Galathea Its structure and relation to the porcelain crabs The 

 two common porcelain crabs Their structure and habits The 

 hermit-crabs The northern stone crab and its relation to the true 

 crabs The masked crab. 



Reptant Crustacea form a much larger division than 

 _ the Natantia, for they include the greater number of 

 the long-tailed forms together with the crabs and their 

 allies. Their classification is a matter of some difficulty, 

 for, as already indicated, although crabs and lobsters seem 

 to be widely separated from one another, yet there are 

 transitional forms which connect them together, and make a 

 sharp division impossible. For our purpose it is, therefore, 

 sufficient if we consider the Reptantia as divided into a 

 number of families, without concerning ourselves with the 

 grouping of these families into larger divisions. Following 

 the same order as with the Natantia, we shall begin with 

 simpler or less specialised forms those most nearly related 

 to prawns and shrimps. 



The first family (As-tacidre) is that to which the cray- 

 fishes proper belong. The most important members of it 

 are the fresh-water crayfish (Astacus fluviatilis), a beautiful 

 little creature quite outside our sphere ; the true lobster 

 (Homarus vulgaris), and the Norway lobster (Neplirops 

 norveyicus). The last is never found between tide-marks, 

 but is at certain seasons brought to market in large numbers, 

 and is included here because it is readily obtainable, and is 



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