208 



LIFE BY THE SEASHORE. 



2. Fam. Cyclometopa. 



a. Walking legs all with thin\ Carapace with nine lobes Cancer 

 pointed terminal segments/ pagurus, or edible crab. 



long as \ P. variegatus is only 

 rtumnus J species. 

 Last segment of ^ 

 fifth legs only ! Only species is 

 expanded j 0. mcenas. 

 Carcinus . J 

 Penultimate seg-^ ,.- 

 ment expanded I m ^ S P 6C1 S > e ^' 

 as well as last f ^-P^e^Pmar- 

 , -Portunus J moreus > etc ' 



3. Fam. Catometopa. 



SUMMARY CLASSIFICATION OF DECAPOD CRUSTACEA. 



I. Natantia swimming forms with compressed bodies and functional 

 swimmerets ; e.g. prawns and shrimps (Chap. VIII. ). Fam. Carididte. 



II. Reptantia creeping forms, sometimes with long tails (Macrura), 

 e.g. lobster and crayfish ; sometimes with inturned tails (Brachyura), 

 e.g. crabs ; intermediate forms also occur. The following families 

 are included : 



(1) AstacidjB, lobster and Norway lobster. 



(2) Palinuridse, rock -lobster. 



(3) Porcellanidse, the lobster-like Galatheas and the crab -like 



porcelain-crabs. 



(4) PaguridjB, the hermit-crabs. 



(5) Lithodidae, the stone-crab, with large incompletely calcified 



abdomen. 



(6) Corystidse, the masked crab and the circular crab ; the latter 



is sometimes placed in the family Cyclometopa. 



(7) Oxyrhyncha, the spider-crabs, apt to be confused with the 



stone-crab. 



(8) Cyclometopa, the shore crab, swimming crabs, and edible crab. 



(9) Catometopa, the pea-crab, and a few other southern forms. 



NOTE ON DISTRIBUTION. 



Generally speaking it may be said that the crabs increase in number 

 'in the British area as one passes southward. Exceptions to this rule 

 are the interesting stone-crab, a northern species, and the two species 

 of Hyas. These last are not absent from the South-west of England, 

 but they are not nearly so abundant there as in the North. On the 

 other hand, the rocky coasts of Devon and Cornwall produce Maia 

 squinado, especially abundant in Cornwall, the velvet-crab between 

 tide-marks, and a number of other interesting and peculiar forms of 

 which no mention has been made here. The shore crab, the edible 

 crab, the numerous species of Portunus apart from the velvet-crab, 

 occur at all parts of the coast. 



