XI 



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 prop-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 (Palasozoic) 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. (Fi-oni Lang's 

 Comparatiee Anatomy.) 



FKI. 503. Phrynus (Pedipalpi). (From Cuvier's Anlnin! A" <',<</*'<.<.) 



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

 in some of their external features between the Scorpions and the 



