HALF AN HOUR WITH CRUSTACEA. 237 



also among the rocks at low tide. It is very 

 sluggish in its habits, and soon dies when taken out 

 of the water. The rays and codfish feed largely on 

 it, and it may often be taken from the stomachs of 

 those fish. The " Pour-horned Spider-crab " (Pisa 

 tetraodon, Fig. 128) has also a triangular-shaped 

 back or carapace, with a series of strong spines 



Fig. 128. 



The Four-horned Spider-crab (male) (Pisa tetraodori), nat. size. 



along the margin. The legs are shorter and stouter 

 than in the previous species. Its name is derived 

 from the four stout spines which project in front, 

 near the eyes. Like the Hyas, it has generally a 

 parasitic growth of algae and zoophytes on its shield. 

 Of the great crab (Cancer pagurus) no description 

 is needed beyond our stating that this is the 



