SAND-FLEAS, &c 187 



for the new shell ; for they immediately begin to grow 

 smaller after the moulting, and soon entirely disappear. 

 The Craw-Fish, or Fresh-water Lobster, much re- 

 sembles the American Lobster, but is only three or 

 four inches long, and lives in brooks. One kind is 

 common on the Western prairies, where it lives in 

 holes which it digs in the ground deep enough to find 

 water. 



SAND-FLEAS, &c., OR FOURTEEN-FOOTED CRUS- 

 TACEANS. 



Beach- or Sand-Fleas are little shrimp-like crusta- 

 ceans which are very common on the sea-beach. They 



Fig. 349. Sand Flea. Fig. 350. Trilobite. 



have seven pairs of feet. Closely related to these are 

 the curious Trilobites, found imbedded in the solid 

 rock, and which lived and died ages ago. 



BARNACLES AND HORSE-SHOE 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 provided 



