444 



ARTHKOPODA. 



Order I. Xiphosura. 



Cephalothorax large ; abdomen terminated by a long spiniform telson. 

 Limulus polyphemus of our east coast, commonly known as king crab 



FIG. 457. FIG. 458. 



Fio. 457. Limulus polyphemus.* horseshoe crab (orig.). 

 FIG. 458. Ventral surface of Limulus moluccanus. (From Ludwig-Leunis.) 



chelicerse ; 2-5, walking feet ; 6', pushing foot ; 6 a , flabellum ; 7, genital" operculum 

 8, gills (there should be five) ; P, base ' ' 



of telson. 



or horseshoe crab. Other species on eastern shore of eastern continent. 

 They burrow beneath the sand and mud of the bottom and feed on worms. 

 In the spring they come to the shore to lay eggs. 



Order II. Eurypterida. 



Extinct Silurian and Devonian forms with small cephalothorax and 

 large twelve-jointed abdomen. The animals are intermediate between the 

 xiphosures and the scorpions. Eurypterus; Pterygotus. some species 

 seven feet long. 



Sub Class II. Arachnida. 



Under this name are included a number of orders of greater or 

 less extent which can be arranged around the spiders, or Aranea, 

 as a centre. There is considerable modification of form, and the 

 following account applies only to the more typical groups. In 

 these the cephalothorax and abdomen are separated by a distinct 

 line, and since the abdominal appendages almost entirely disappear 

 in the adult, the number of somites can only be ascertained where 

 their boundaries are evident. The number varies between six in 

 the phalangids and thirteen in the scorpions. 



The cephalothorax is, except in the Solpugidae, a single piece- 



