154 



GENERAL ZOOLOGY 



allied to the Crustacea. They are named trilobite from the 

 apparent division of the body longitudinally into three parts. 

 The length of the body varied from one 

 inch to two feet. They are thought to 

 have lived in shallow Avaters along shores, 

 and through a long period of the earth's 

 history must have been a most character- 

 istic feature of the fauna of the world. 

 Of the many species of trilobites of which 

 we find fossils, not one remains at the 

 present day. 



THE HORSESHOE CRABS: XIPHOSURA 



FIG. 80. Trilobite The large, crab-like animal shown in 



(From Report of Geolog- Fig. 81 is variously known as the horse- 



ical Surve 

 Kingdom) 



shoe crab, the king-crab, the horsefoot, 



and by its scientific name, Lim'ulus poly- 

 phe'mus. The first and last common names are derived from 

 the shape of the cephalothorax. A pair of simple eyes is 

 placed near the median dorsal line ; a pair of large com- 

 pound eyes is on the sides of the cephalothorax. There are 

 five pairs of legs on the under surface of the cephalothorax. 

 Several pairs of plate-like gills are attached to the under 

 surface of the abdomen. The body is terminated by a long, 

 spear-shaped spine, which characteristic gives the group 

 its name, Xiphosu'ra (Gr. xiphos, sword; oura, tail). 



Liniulus is found in sheltered bays and estuaries along our 

 eastern coast from Maine to Florida, and on the coasts of 

 the West Indies and Mexico. In places where it is most 

 abundant it is caught with rakes, killed, dried, and used 

 as a fertilizer. It is also used for baiting eels and other fishes. 

 Its practical extinction is threatened in many places. 



The illustration shows the horseshoe crab almost buried 

 beneath the sand through which it is plowing in search of 



