MUSEUM OF COMPARATIVE ZOOLOGY. 267 



Fig. 5. A short disk-stump covered by a thick epidermis ; *^. 



Fig. 6. Three disk-stumps, one with and two without epidermis ; ^ Q . 



Fig. 7. Edge of a side arm-plate near tip, carrying two spines and a double 

 hook ; *)&. 



Fig. 3. Under arm-jilates ; $. 



Fig. 9. Ophiothrix Martensi. Hook and arm-spine next above it, with its 

 epidermis ; s j L . 



Fig. 10. Upper arm-spine and upper arm-plates close to disk ; showing the 

 central blue line with a white line on each side. 



Fig. 11. Ophiopsammium Sempcri. Twelfth joint, seen diagonally from below, 

 showing, on the further side, an extended tentacle and the lowermost arm-spines ; 

 and, on the nearer portion, a side arm-plate and its spines, foreshortened, and 

 with tin.' tentacle omitted ; - 2 / 1 . 



Fig. 12. Part of upper surface of disk, showing the base of an arm, and the 

 pairs of spines in the interbrachial space ; -f. 



Fig. 13. Tooth-papillae and teeth seen from within ; \". 



Fig. 14. Longest arm-spine (third) near base of arm ; \". 



Fig. 15. Under arm-plates, as they may be distinguished near tip of arm ; 1 , Q . 



Fig. 16. Joints, seen from above, close to end of arm, showing the beginning 

 of the granulation, and the embryonic upper arm-plates ; each side arm-plate is 

 furnished only with two little arm-spines and a strong double hook ; ^ 



Fig. 17. Granulation of the upper arm near its base ; ■ 2 1 Q . 



Fig. 13. Amphiura lavis. A portion of the disk, from above, with the base 

 of an arm ; x ^-. 



Fig. 19. An angle of the mouth, showing the four mouth-papilk~e on each side, 

 with mouth-shield and side mouth-shields ; -^ 



Fig. 20. Two joints of arm, near the disk, seen from below ; x y. 



Fig. 21. Ophiocnida echinata ? Part of a side arm-plate with its spines ; *-. 



Fig. 22. A portion of the disk, from above, with the base of an arm ; ^-. 



Fig. 23. An angle of the mouth, with a mouth-shield and the first two under 

 arm-plates ; f. 



Fig. 21. Op7iiot7irix cxigua. Upper arm-plates and bases of the arm-spines, 

 near the disk ; -\^. 



Fiu r . 25. The common form of disk-stump ; -"-. 



Fig. 20. Hook, standing below the arm-spines : s f-. 



Fig. 27. Ophiothrix comata (from the original in the Vienna Museum). An 

 under arm-plate, with its tentacle-scale ; - ] ". 



Fig. 2^. Two upper arm-plates, with the liases of arm-spines ; J ,°. 



Fig. 29. OphiotJirix ciliaris (from the original at the Garden of Plants). A 

 portion of upper surface of disk and two upper arm-plates, showing the distribu- 

 tion of the fine disk-stumps ; ?. 



Fig. 30. A disk-stump, from near the edge ; *£. 



Fig. 31. Two under arm-plates. 



