OCR Text |
Show 1892.] CLASSIFICATION OF OPHIUROIDS. 181 most kindly informs me the arm-ossicles remind him most of those of Ophiothrix and Ophiacantha. The Streptophiurae 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. Ophiohelus. 5. Ophiotholia (?). II. Radial shields present. 6. Ophioscolex. 7. Ophiambix. 8. Ophiogeron. 9. Ophiobyrsa. 10. Ophiomyxa (pars). ft. Upper arm-plates minute or formed of scattered plates. 11. Ophiomyxa (pars). 12. Ophiomyces. 13. Ophiochondrus. 14. Hemieuryale. 15. Sigsbeia. It will be gathered that I regard the simple-armed Astrophiurae 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. Ophiocreas. 7. Astroschema. 8. Astroceras. B. Arms branch a few times near their free ends. 9. Trichaster. 10. Astroclon. 11. 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-Astronycinae, Trichasterinse, and Gorgonocephalinae ; and the fact that it should be so, notwithstanding the multiplication almost by three of the genera of Astrophiurae since 1866, is another |