1892.] CLASSIFICATION OF OPHIUROIDS. Igl 



most kindly informs me the arm-ossicles remind him most of those 

 of Ophiothrix and Ophiacantha. 



The Streptophiurse may be thus arranged : — 



A. No under arm-plates 1. Ophioteresis. 



B. Under arm-plates imperfect . . 2. Ophiosciasma. 



C. Under arm-plates moderate or well developed. 



a. No upper arm-plates. 



I. No radial shield . . 3. Neoplax. 



4. OpMohelus. 



5. Ophiotholia (?). 

 IT. Radial shields present. 



6. Ophioscolex. 



7. Ophiamhix. 



8. Opliioge7'on. 



9. Ophiobyrsa. 



10. OpMomi/.va (pars). 



/5. Upper arm-plates minute or formed of scattered plates. 



1 1 . Ophiomycca (pars). 



12. Ophiomyces. 



13. OpMochondrus. 



14. Hemieuryale. 

 1.5. Sigsbeia. 



It will be gathered that I regard the simple-armed Astrophiurse 

 as the more archaic, and I propose, therefore, an arrangement of the 

 genera which is altogether different from that of Mr. Lyman :— 

 A. Arms simple. 



i. Disk large I . Astrotoma. 



2. Astronyx. 

 .. 3. Astrochele. 



u. Disk moderate (about one-tenth of the length of the 



^^'"^) 4. Astrogomphus. 



... 5. Astroporpa. 



in. Disk small, even very small. 



6. Ophiocreas. 



7. Astroschema. 

 -n . 8. Astroceras. 

 a. Arms branch a few times near their free ends. 



9. Trichaster. 



10. Astroclon. 



11. Astrocnida. 

 L. Arms branch much and from near their base. 



12. Euryale. 



13. Gorgonocephalus. 



14. Astrophyton, 



These three groups (A, B, and C) correspond to the subfamilies 

 of Ljungman--A8tronycin^ Trichasterinae, and Gorgonocephalinse ; 

 and the fact that It should be so, notwithstanding the multiplication 

 almost by three of the genera of Astrophiurse since 1866, is another 



