Palaeozoic Arachnida of North America. 29 



+ cucullus absent 5 



5. All segments of the cephalothorax fused together .... 7 

 + two or three posterior segments of the cephalothorax 



free. Mandibles always chelate 6 



6. Only 2 posterior cephalothoracic segments free. Ab- 

 dominal segments 11, the last with a segmented whip 



Palpigradi 



+ three cephalothoracic segments free. Abdominal 



segments 10. No whip Solifugae 



7. Abdomen with petiolus 8 



+ abdomen broadly joined to the cephalothorax 10 



8. Coxae of pedipalpi completely fused together, forming 

 a triangular plate. Pedipalpi chelate. Coxae of legs 

 radiating from the central sternum, equal in size. All 

 legs thin and long Kustarachnae 



+ Coxae of pedipalpi not fused into one plate 9 



9 Pedipalpi raptorial ; i st pair of legs transformed into an 

 antenniform sense organ. No spinning organs 



Pedipalpi 



+ Pedipalpi pediform ; ist pair of legs not transformed 



into an antenniform sense organ. Spinning organs 



in abdomen Araneae 



10. Pedipalpi powerful, chelate. Chelicera chelate. Spin- 

 ning glands in front or behind the genital openings, their 

 ducts opening on movable finger of chelicera 



Pseudoscorpiones 

 + Pedipalpi not chelate. Spinning glands absent . . . .11 



11. Abdomen not segmented (with exception of the sub- 

 order Notostigmata in which there are 4 dorsal abdominal 

 stigmata). Coxae of all legs devoid of maxillary lobes 



Acari 

 + abdomen clearly segmented 12 



12. Coxae of the ist pair of legs and often also of the 2d and 

 3d pair with maxillary lobes. Chelicera chelate. Ab- 

 domen composed of 10 segments, the 10 th being re- 

 presented by the operculum, but the number of visible ter- 

 gites and sternites is usually smaller, owing to a fusion of 

 the anterior segments with the cephalothorax 



Opiliones 

 + all coxae without maxillary processes 13 



13. Tarsi and metatarsi of ist pair of legs converted into 

 a 7-jointed tactile organ. Abdomen composed of 11 seg- 



