Mesostigmata 109 



Key to the Uropodina 



1. Camerostome present 2 ^ 

 Camerostome absent Discourellidae 



2. Dorsal plate restricted to dorsal surface 3 ^ 



Dorsal plate extends laterally and ventrally so that only central 

 portion of ventral surface not covered by dorsal plate 



Coxequesomidae 



3. Ventral, posterior, marginal plates absent 4 

 A pair of ventral, posterior, marginal plates present Planodiscidae 



4. Dorsal marginal plate present 5 -' 

 Dorsal marginal plates absent Circocyllibanidae 



5. Stigmata opposite coxae ii or between ii and in 7 " 

 Stigmata opposite coxae iii 6 



6. Tritosternum covered by coxae i Trematuridae 

 Tritosternum not covered by coxae i Cillibidae 



7. Anterior ends of marginal plate fused with dorsal plate anteriorly 8 



Anterior ends of marginal plate not fused with dorsal plate 



Trematurellidae 



8. Depressions to accommodate legs present 10 

 Depressions to accommodate legs absent 9 



9. Distinct posterior dorsal plate present Eutrachytidae 

 Posterior dorsal plate not distinct Prodinychidae 



10. Posterior dorsal plate absent 11 \ 

 Posterior dorsal plate present Urodiaspidae 



11. Marginal plates fused with dorsal plate 12 

 Marginal plates fused with ventral plate Trachyuropodidae 



12. Marginal plate completely surrounds dorsal plate 13 

 Marginal plate reduced posteriorly Phaulodinychidae 



13. Marginal plate scalloped on its inner border Urodinychidae 

 Marginal plate not scalloped Uropodidae 



