786 



CLASS V. ARACHNID A. 



Eurypterida. A spine-like or plate-like telson terminates the 

 body. 



The Xiphosura consists of the recent species of King Crabs, 

 with some allied fossil forms, but no remains of the Eurypterida 

 have been found subsequent to the Carboniferous period. 



Order 1. XIPHOSURA. 



Merostomata with the abdomen consisting, in the. recent members, 



of six fused seg- 

 ments anteriorly, 

 bearing six bira- 

 mous appendages, 

 and of an unseg- 

 mented posterior 

 regio n. The 

 seventh cephalo- 

 thoracic appen- 

 dages (chilaria) 

 are distinct and 

 unsegmented. 



The body of 

 L i m u I u s, the 

 King Crab or 

 Horseshoe Crab, 

 is divided into 

 three parts which 

 may be called, 

 without implying 

 an exact homo- 

 logy with parts 

 s o n a m e d in 

 other groups, the 

 cephalo thorax, 

 abdomen and 

 caudal spine. It 



FIG. 510. Dorsal view of Limulus polypJtemusx J. 1 cephalo- J S COVei'eCl \\ltll 

 thorax; 2 abdomen; 3 caudal spine: 4 median eyes; 5 , f i 



lateral eyes (from Shipley and MacBride). 



