MUSEUM OF COMPARATIVE ZOOLOGY. 271 



Fig. 4. Side arm-plate (third joint from the disk) with its spines, and a corner 

 of the upper arm-plate ; 5- 



Fig. 5. Ophiura hvvis (Mediterranean). The skeleton of the mouth-parts, 

 and of the arm as far as the edge of the disk, with the genital plates, o, o, in po- 

 sition, seen from above; f. c, jaws; e, jaw-plate; d", teeth; u, circular canal for 

 the nerve-ring of the mouth ; r, r', sockets of the second and first pairs of tenta- 

 cles; q, tentacle-scale of the first pair; /, mouth-frames; r, r (on the arm-bones), 

 places for the tentacles ; s, one of the supplementary pieces lying along the margin 

 of the disk, under the skin ; V upper arm-canal. On the left are a few scales of 

 the disk, in position, with their coat of grains. The radial shields are removed. 



Fig. 6. Jaws, one mouth-frame, and two arm-bones in profile, the latter are 

 separated and turned so as to show part of the top ; lettering as above ; j. 



Fig. 7. Inner side of first arm-bone, showing its points, which articulate with 

 the outer side of the mouth-frames (compare Fig. 6) ; t, lower arm-canal ; h, under 

 arm-] date ; u; lower muscle-field ; ^. 



Fig. 8. Fifth arm-bone, outer side, with tentacle-sockets, r, upper and lower 

 canal, articulating peg, and depression to receive the umbo of the next arm- 

 bone; y. 



Fig. 9. Inner side of same bone, with the lower muscle-field, w, the articulating 

 umbo, and the depression below it to admit the articulating peg ; j. 



Fig. 10. Same bone from below, with the muscle-field, v, on the inner side, 

 and the tentacle-socket, r, on the outer, where also is the articulating peg; on the 

 median line runs the lower arm-canal, t ; j. 



Fig. 11. Ophioglypha cileata (Mediterranean). Skeleton of arm and mouth- 

 parts, to edge of disk, seen from above, with a genital plate, o, in position on one 

 side, and on the other a radial shield, J, turned aside to show the underlying parts. 

 On the middle line is the first upper arm-plate, j; on one side of it is the lower 

 arm-comb, in' ; and, on the other, the upper arm-comb or radial scale, m. Other 

 letters as above ; y. 



Fig. 12. Three innermost side arm-plates, i, forming one wall of the genital 

 opening. The upper corner of the side mouth-shield, b, supports the inner end 

 of the genital plate, o, here seen in profile, with the under arm-comb, m! (com- 

 pare Fig. 11), q, tentacle-scales; f. 



Fig. 13. Ophiothrix quinqueinaculata (Mediterranean). Skeleton of mouth- 

 parts and arm, as far as edge of disk, witli a radial shield and genital plate ar- 

 ranged and lettered as in Fig. 11, except that the mouth-frames are separated 

 from the innermost arm-bone ; •}. 



Fig. 14. Outer articulating surface of mouth-frames (compare Fig. 13) ; ^. 



Fig. 15. Inner articulating surface of t he arm-bone next tie' mouth-frames : -> 



Fig. 16. Ophiothrix alopecurus (Adriatic). An arm-bone close to the tip of 

 the ami, seen from above, with a side arm-plate in position, and bearing a hook 

 ami the bases of three young spines ; 3 f-. 



Fig 17. The same bone from below ; 3 f-. 



