126 Papers from the Marine Biological Laboratory at Tortugas. 



Plate 3. 

 Figs, i to 10. — Lowest arm spine of Ophiothrix angulata {Say). Xioo. 



Fig. I. From first (next to terminal plate) segment. 



2. From second segment. 



3. From third segment. 



4. From fourth segment. 



5. From sixth segment. 



6. From middle portion of the arm (any segment). 



7. From twelfth segment, counting from mouth. 



8. From ninth segment from mouth. 



9. From sixth segment from mouth. 



10. From third segment from mouth. 



These spines are all shown in the same position. Figure 6 shows the appearance 

 of the typical spine characteristic of the genus; figures 1-5 show its development, 

 and figures 7-10 its senescence. Spines, like figures 9 and 10, are very httle 

 different from the ordinary arm-spines. ^, . . \ r u- 1 



11. Next to the lowest arm-spine of Amphipholis squamata (Delle Chiaje) from third 



segment, counting from tip of arm. X375- 



Figs. 12 to 14. — Lowest arm spine of Ophiactis savignyi (M. & T.). X375» 



Fig. 12. From third segment from tip of arm. 



13, From sixth segment. 



14. From middle of arm (any segment). 



Figs. 15 to 19. — Ophiothrix angulata {Say). 



Fig. 15. Torus of specimen 2 mm. across disk. X90. 



16. Torus of adult, 5 mm. across disk. X40. ... 



17. Torus, teeth, and dental-papillae of young, 2 mm. across disk, seen trom the side. 



18. Central plate, radial shields, and part of disk of a specimen 2 mm. across disk. 



X40. 



19. The same of a specimen 3 mm. across disk. X40. 



