CEUSTACEA. 125 



P. squilla and P. varians, which both differ a little 

 from the former. 



There is a kind of shrimp belonging probably 

 also to the genus Palemon, and which is about seven 

 inches long ; it is very common at the mouths of 

 rivers in Florida. Leba has called it the American 

 craiufish, but it is probably the Palemon setiferus 

 (Olivier) of naturalists. 



Shrimps and their allies are the principal sca- 

 vengers of the ocean; they clear away the decom- 

 posing animal matter which floats in the sea. They 

 are highly prized as a delicious and nutritive article 

 of food, and might be easily reared artificially or 

 cultivated, as crawfish and lobsters have been in 

 France, were it deemed profitable or necessary. 



Curious little parasitical Crustacea belonging to 

 Latreille's genus Bopyrus are found living upon 

 prawns. Those who are in the habit of eating 

 prawns will probably have sometimes observed a 

 tumour under the carapace on one side of the 

 animal. On lifting this part of the shell, the para- 

 site will be discovered immediately under it, upon 

 the branchiae or gills. These little beings belong 

 to the family of Isopoda. The species which live on 

 our common prawn is Bopyrus crangorum. The 

 former does not appear to suffer at all from the 

 invasion of this parasite, which will one day, doubt- 

 less, turn out to be the larvce of some other 



