AKTHKOPODA. 81 



Order VI. XIPHURA. 



PCECILOPODA. XYPHOSUKA. MEROSTOMATA. 



Head not distinct from the thorax, covered by a carapace. A 

 styliform process or tail terminating the abdomen. Legs six 

 pairs, surrounding the mouth. 



The basal joints of the legs surrounding the mouth represent 

 mandibles and maxillae, the rest of the joints are ambulatory and 

 prehensile. The young have no tail, which in the adult equals 

 the rest of the body. There are two eyes, with two ocelli. The 

 eyes are not faceted. 



The embryo in its latest stage is said to resemble certain Trilo- 

 bites. Only one recent genus is known, which existed also in the 

 Oolitic period. The other fossil genera occur chiefly in the coal- 

 formations. 



Limulus (King-crab). 

 *Belinurus. 

 *Cyclus=*Halicyne. 



Order VII. EURYPTERIDA. 



Head with two large marginal eyes and two median ocelli. 

 Body of numerous free segments (12), all, except the first two, 

 without appendages. 



These were marine animals, often of large size, belonging 

 to the Pakeozoic period. They are allied to Limuhts and 

 Trilobita, and, according to Van Beneden, cannot be separated 

 from the Scorpions. They had only one pair of antennse. 

 'Pterygotus angiicus is known to the Scotch quarry men. as the 

 " Seraphim." 



Sclunarda makes this order a pendant to Xiphura. The two 

 are joined by Claus to Phyllopoda, which comprises, according 

 to him, as suborders, Cladocera and Branchiopoda. Branchio- 

 poda, however, is by other authorities made to include Phyllo- 

 poda as well as Ostracoda and Trilobita. 



Woodward has enumerated sixty-two species. 



*Eurypterus. *Stylonurue. 



*Pterygotus. *Hernirhypis. 



