MACROUROUS DECAPODS. 253 



862. The MACROURA, or long- tailed Decapods, are dis- 

 tinguished not merely by the length of the tail, but by having 

 it terminated by a sort of fin, expanded laterally, and consisting 



FIQ. J8S. PALINURU8. 



of five pieces (Fig. 586). This is a very powerful instrument 

 for motion in water, serving, by its vertical strokes, to propel 

 the animals through the liquid ; and we consequently find the 

 Crustacea of this Section much more frequently swimming in the 

 water than walking on its bottom or on the shore. This Section 

 is a very extensive one, and contains the largest species of the 

 whole class. The Lobsters, Cray-fish, Prawns, Shrimps, &c., 



