PHYLUM ARTHROPODA 



613 



ORDER 9. EURYPTERIDA. 



Arachnida with a relatively small cephalothorax, followed by 

 twelve free segments and a terminal, elongated, narrow telson. 

 There are a pair of prse-oral leg-like or chelate appendages and 

 four more leg-like appendages on the cephalothorax, the last 

 expanded to form swimming paddles. A broad operculum is 

 situated immediately behind the cepha- 

 lothorax. There are pairs of lamellate 

 appendages on certain of the anterior 

 free segments. The exoskeleton is char- 

 acteristically sculptured. 



This order includes only a number of 

 extinct (Palaeozoic) forms of large size 

 (Fig. 512). 



3. GENERAL ORGANISATION. 



The external form in the Scorpionida 

 has already been sufficiently described. 

 Most nearly related to that order in this 

 respect are the Pseudoscorpionida or 

 Book-scorpions and their allies. In these 

 (Fig. 502) there is an unsegmented 

 cephalo-thorax, or the carapace is crossed by two transverse grooves 

 which may indicate segmental divisions. There is a broad abdomen 

 consisting of eleven, or more rarely ten, segments; the post- 

 abdomen is not represented, nor the caudal sting. The chelicerse 

 are small; the pedipalpi are large, and resemble those of the 

 Scorpions in their chelate form. Spinning glands are present. 



FIG. 502. Chelifer bravaisii. 



2 6, second to sixth pairs of 

 appendages. (From Lang's 

 Comparative Anatomy.) 



FTO. 503. PhryxiUS (Pedipalpi). (From Cuvier's Animal Kingdom.) 



The Pedipalpi, or Scorpion-spiders , (Fig. 503), are intermediate 

 in some of their external features between the Scorpions and the 





