CRAY-FISHES. LOBSTER, &c. 77 



plates arranged like a fan. They are essentially swimmers, and 

 never land ; they never walk except at the bottom, under water ; 

 they swim almost constantly, and by striking the water with their 

 powerful tail, dart forward with great rapidity. The body 19 

 elongated, and almost always laterally compressed; they hav^ 

 very long antennae, and false natatory legs beneath the abdomen 

 This section of decapods is divided into four families : Cray or 

 craw-fish, Lobsters, Locustse, and Prawns. 



10. Cray-fishes are distinguished from most other decapods by 

 the conformation of their legs ; those of the first pair terminate 

 in very large chela3 or pincers; and those of the two succeeding 

 pairs, although slender, also terminate in pincers. The carapace 

 is a little elongated, and is not armed with spines, and its anterior 

 extremity is always extended so as to form a kind of beak or 

 projecting rostrum (Jig. 65, r). These crusta'ceans are aquatic ; 

 some live in fresh water, and others inhabit the sea. 



11. The fresh-water cray-fish (Astacus fluviatilis) is found in 

 the fresh waters of most countries of Europe, and ordinarily 

 keeps under stones. It feeds on mollusks, fishes, putrid flesh, 

 &c. It is said to live more than twenty years ; those found in 

 running waters are most esteemed. 



12. The sea cray-fish or lobster Astacus marinus (fig. 61) 

 is much larger than the fresh-water or river cray-fish ; like the 

 locustse, it frequents fissures among rocks. The American species 

 is somewhat different from that of Europe. Lobsters are caught 

 in traps, made of slats or osiers, baited, and then sunk by means 

 of a weight ; a buoy and cord are attached to draw up the trap 

 for examination, at the proper lime. 



13. The locustoe (Palinu'rus) are the largest of all the deca- 

 pods of this section. Their carapace is studded with a great 

 number of spines, and terminated by two thick points curved 

 forwards ; the abdomen is very large ; their legs are all termi- 

 nated by a single toe ; those of the first pair are strongest, but 

 shorter than those of the second pair. These crusta'ceans inhabit 

 almost every sea, and are sought as food. The Palinu'rus quad- 

 ricornis is sometimes half a yard in length, and when loaded 

 with ova weighs from twelve to fourteen pounds. 



14. Prawns Pal&mon (fig- 65) are small decapods, having 

 an elongated, laterally compressed body ; the legs are slender, 

 and those of the two first pairs are terminated by little pincers , 



10. How are cray-fishes distinguished ? 



1 1. Do all cray-fishes live in salt water ? 



12. What are lobsters? 



1 3. What are locustse ? 



14. What ar^ prawns? 



