THE DECAPOD CRUSTACEA. 169 



tKe preceding joint, which formed the other half of the 

 forceps. In the shrimp the prolongation of the penultimate 

 joint is very minute, and the last joint is bent down sharply 

 upon the preceding joint ; this condition is described as sub- 

 chelate. The next pair of legs in the shrimp are very 

 slender and end in chelae ; the remaining legs end in simple 

 claws. 



The common shrimp can be recognised by the following 

 special characters. The carapace has three spines only, a 

 median and two lateral; the abdomen is perfectly smooth, 

 and regularly marked with brown spots. It is the largest 

 British member of its genus, and reaches a length of two 

 and a half inches. 



The great size of the antennal scales is a very obvious 

 feature of the shrimp, and it is interesting to note that in 

 burying itself it first makes an excavation by rapid move- 

 ments of the legs, and then completes the process by 

 shovelling sand over the body by means of the antennal 

 scales. It is a matter of common observation how complete 

 the burying process is. 



This completes the description of the common types of 

 Natant Decapods. It should be clearly understood that 

 there are other British genera besides those described, but 

 specimens of them are rare in Britain, and have been 

 omitted. The descriptions given above will be sufficient to 

 make plain the general characters of these Crustacea as con- 

 trasted with the creeping forms next to be described. 



