FOURTEEN-FOOTED CRUSTACEANS. 



20I 



for the new shell ; for they immediately begin to grow 

 smaller after the moulting, and soon entirely disappear. 

 The Crawfish, or Fresh-water Lobster, much resem- 

 bles the American Lobster, but is only three or four 

 inches long, and lives in streams and lakes. One kind 

 is common on the western prairies ; it lives in holes 

 which it digs in the ground deep enough to find water. 



Sand Fle.4s, etc., or Fourteen-footed Crustaceans. 



Beach, or Sand, Fleas are little shrimp-like Crusta- 

 ceans, common on the seabeach. They have seven 



Fig- 349- — Sand Flea. 



Fig. 350. — Trilobite. 



pairs of feet. Imbedded in the rocks are found the 

 curious, closely related Trilobites, which lived ages ago. 



Barnacles and Horseshoe Crabs. 



The Barnacles are of many kinds. Some resemble 

 bivalve shells, and grow in clusters, attached by stems, 

 as seen in Figure 351 ; others, as in Figure 352, are 

 acorn-shaped, and are fixed directly upon the rocks, 

 shells, lobsters, or ship-bottoms. They are all pro- 

 vided with feather-like arms or feet, which they regu- 



