PLAGIOSTOMES. 



353 



general form, which differs but little from that of 

 ordinary fishes. Their skin is covered with a mul- 



FlG. 285. HAMMER-SHARK AXD SAW-FISH. 



titude of small spines of stony hardness, and becomes 

 very rough on drying, so as to form a sort of file 

 (shagreen), much employed in the arts for polishing 



FIG. 286. SHARK'S EGG. 



