100 CRUSTACEA. 



not concealed, but simply bent under tin- breast, and termi- 

 nated by a fan-like apparatus or swimmeret, having also, <m 

 its under side, five pairs of small appendages or false legs, 

 with two filaments at tbe extremity of* each. The abdomen 

 is always seven-jointed, the antennae generally long and ex- 

 serted, the outer foot-jaws long, and not entirely covering 

 the inner parts of the mouth. The shell, or carapax, is 

 longer and narrower than in the Brachyura, or crab.-, and 

 generally terminated in front by a spine. These Crus- 

 tacea are marine, and do not quit the water like the land 

 crabs. 



This sub-order is divisible into five families, namely : 



1. Hippidce. 



2. Paguridee, or hermit crabs. 



3. ScyllaridaE, including the scaly lobsters, Palinurus. 



4. Astacida, or lobsters and crayfish, including the 



Galathece and Porcellance. 



5. Paleemonidce, or shrimps. 



The hermit crabs are of very common occurrence upon 

 tin- shore, and are well known from their singular and soli- 

 tary mode of life, which is passed entirely in old and for- 

 saken univalve shells, exhibiting a most beautiful instance of 

 that connexion which is always found to exist between the 

 structure and functions of animals; hence it is that \\e >ee 

 the reason why the abdomen of these crabs is of a soft and 

 fleshy nature, since, if it were hard and shelly, like that of 

 the lobster, it would be impossible for it to accommodate 

 itself to its tortuous abode, whereby it is enabled to escape 

 from those dangers to which it would be exposed from tin- 

 boisterous element in which it resides, if it were not thus 

 amply secured from harm. The species of \vhieh this i. p enns 

 is composed are very numerous, and arc found in all parts of 

 the globe. 



