1892.] CLASSIFICATION OF OPHIUROIDS. 181 



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

 of OpMothrix and Ophiacantha. 



The Streptophiurae may be thus arranged : — 



A. No under arm-plates 1. Ophioteresis. 



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

 Vj. Under arm-|)lates moderate or well developed. 



a. No upper arm-plates. 



I. No radial shield . . 3. Neoplaoc. 



4. Opliiohelus. 



5. Ophiotholia (?). 

 II. Radial shields present. 



G. Ophioscolex. 



7. Ophiainhiv. 



8. OpMogeron. 



9. Ophiobyrsa. 



10. Ophiomyxa (pars). 



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



1 1 . Ophiomy.va (pars). 



12. Ophiomyces. 



13. Ophiochondrus. 



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 1 . Astrotoma. 



2. Astronyx. 



3. Astrochele. 



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

 arms) 4. Astrogomphus. 



5. Astroporpa. 

 iii. Disk small, even very small. 



6. Ophioereas. 



7. Astroschema. 



8. Astroceras. 



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



9. Trichaster. 



10. Astroclon. 



1 1 . Astrocnida. 



C. 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 — Astronycinse, Trichasterinae, and Gorgonocephalinse ; 

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

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



