Growth-changes in Brittle Stars. 125 



LIST OF PLATES. 

 EXPLANATION OF LETTERING. 



A = Ala. P = Protapophysis. Zc = Zygocoele. 



AH = Anterior hypapophysis. Pa = Parapophysis. Zg = Zygapophysis. 



E = Epanapophysis. PH = Posterior hypapophysis, Zp = Zygophore. 



Ep = Epapophyses. T = Taphrus. Zt = Zygotreme. 



LAR = Lower alar ridge. UpAR = Upper alar ridge. Zy = Zygantrum. 

 MH = Median hypapophysis. Z = Zygosphene. 



Plate i. 

 Ophiaciis savignyi (M. & T.). 



Fig. I. A young individual, showing bases of 3 arms, and 3 very youthful arms, of which 

 the median is evidently the youngest. X40. 



2. Disk of smallest individual seen, showing primary plates on older portion. X40. 



3. Mouth of a young specimen, showing 2 old jaws and 3 pairs of old oral tentacles, 



and 4 young jaws. X90. 



4. Side view of a young jaw with 4 teeth and an old jaw with 5; 2 oral tentacles are 



also shown. X90. 



5. Torus of a young individual. X90. 



6. Fourth segment from tip of arm, showing skeletal parts, as seen from below. X90. 



7. A very young arm, with only one segment; seen from below. X90. 



8. Vertebra of fifty-fifth segment from mouth in an arm with 70 joints; seen from 



above. X40. 



9. Vertebra of fiftieth segment of same arm; from above. X40. 



10. Vertebra of fortieth segment of same arm; from above. X40. 



11. Vertebra of thirtieth segment of same arm; from above. X40. 



12. Vertebra of tenth segment of arm with only 18 joints; from above. X90. 



13. Vertebra of twentieth segment of arm with 70 joints; from above. X40. 



14. Vertebra of tenth segment of same arm; from above. X40. 



15. Same vertebra as fig. 14; seen from aboral end. X40, 



16. Same vertebra; seen from below. X40. 



17. Same vertebra; seen from adoral end. X40. 



18. Same vertebra; seen from side. X40. 



19. Vertebra of second segment of arm with 70 joints; seen from above. X40. 



Plate 2. 

 Figs, i to 6. — Amphipholis squamata (Delle Chiaje). 



Fig. i. One of the second pair of adambulacral plates, with its adjoining oral tentacle, 

 from a specimen 0.65 mm. across the disk; to show posterior (aboral) spinous 

 projection. X375- 



2. One of the oral plates ("jaw") and its adjoining adoral plate, from a specimen 



0.80 mm. across disk; to show origin of first 2 oral papillae, in connection with 

 them, but from separate centers of calcification. X375. 



3. A jaw, and adjoining parts, from a specimen I mm. across disk; to show Amphiura- 



stagc of development. X90. 



4. A jaw, and adjoining parts, from a specimen 1.35 mm. across disk; to show the 



Amphipholis character attained. 



5. Side view of torus and first tooth, from a specimen 0.65 mm. across disk. X375- 



6. Side view of torus and first tooth, also from a specimen 0.65 mm. across disk but 



somewhat older. X375. 



Figs. 7 to 12. — Ophiolhrix angtilala (Say). 



Fig. 7. Vertebra of sixth segment from tip of arm; from the side. X90. 



8. Typical vertebra; from the side. X40. 



9. Same vertebra; from above. X40. 



10. Same vertebra; showing aboral surface. X40. 



11. Same vertebra; from below. X40. 



12. Same vertebra; showing adoral surface. X40. 



