ARTHROPODA. 



95 



The Scorpions closely resemble in many respects the Xiphura 

 and Euryptericla, from which Van Beneden thinks they cannot be 

 separated. Fabricius placed them with the Crustacea in his 

 order Agonata (Syst. Ent. 1 775). They date back to the Car- 

 boniferous period. 



This is such a homogeneous order that some authors recognize 

 only a single genus. Peters, however, divides it into four groups, 

 depending on the form of the sternum and the armature of the 

 mandibles ; more recently, and on different principles, Thorell 

 makes four families and 31 genera. With Phrynidea they form 

 the Polymerosomata or Pedipalpi of some writers. Combining 

 Vejovis with Scorpionidae (Peters), and Centrums with Aiidroc- 

 tonidae (Thorell), we have three families. 



TelegonidcB. . Androctonidce. 



Bothriurus. Centrurus. 



Telegonus. 

 Cercophonius. 



lurus. 



Heterometrus. 



Scorpio. 



Vejovis. 



Ischnurus. 



*Cyclophthalmus. 



Lychas=Tityua. 

 Isometrus. 

 Buthus. 

 Androctonus = 

 Prionurus. 



Order II. CHELIFEEIDEA. 



PSEUDOSCORPIONES. 



Abdomen segmented, indistinctly separated from the cephalo- 

 thorax, mutic at the extremity. Maxillary palpi longer than the 

 feet, terminating in a didactyle hand with a movable finger. 

 Eyes 2-4. 



Like the Spiders the Cheliferidea are provided with silk-glands, 

 and unlike the Scorpions, which they externally resemble, they 

 have neither a postabdomeu nor poison-glands. They breathe 

 by tracheaa. 



These Arachnids are of small size, and are found chiefly in 

 caverns and damp places in temperate countries. Chelifer can- 

 croides is often to be met with among old books. Owen's order 

 Trachearia comprises this and three co-ordinate groups, " Acarina, 

 Opilionina, and Solpugii." 



ObisiidcB. Cheliferidce. 



Cthonius. Chernes. 



Blothrus. Garypus. 



Obisiuin. Chelifer. 



Boncus. Olpiumu 



