10 COELOPLEURUS FLORIDANTJ& 



the ambitus. On the actinal side the spines of both areas are identical ; 

 they consist of a finely serrate base, above the milled ring, extending half 

 the length of the spine ; the upper part is Hat. spathiform, with sharp 

 edges ; the flat portion of the spine having the amorphous, finely granular 

 {Figs. >,, ;, »;) structure of the large spines already described in the Revision 



Fig. 4. Fig. 5. Fig. 6. Fig. 7. 



of the Echini. As the spines grow older the serrated collar loses its promi- 

 nence (Fit/, r), and the large ambulacral spines of the abaetinal surface appear 

 uniformly granular, with a delicate suture somewhat above the milled ring. 

 The S" sn;i l ,(,( ' curves, so pi'ominent on the abaetinal interambulacral spaces 

 of the Bourbon species, are quite apparent in our largest specimens; the 

 miliaries forming independent patches or triangular figures, extending al- 

 ternately from the median line of the plates towards the poriferous zone. 

 The miliaries carry pedicellarias <>n long, stout stems, like those of Podo- 

 cidaris, with a comparatively small head. The ambulacral suckers are pointed 

 towards the abaetinal pole, as in all Axbaciadae, and have prominent, well- 

 developed suckers on the actinal side. The actinal membrane is hare, with 

 the exception of ten large buccal plates, which carry clusters of small pedi- 

 cellariae. The teeth do nol differ from the teeth of the Bourbon species and 

 of the Axbaciadae. 



The anal and ocular plates carry small pedicellarise and minute rudiment- 

 ary spines. The long collar of the base of the primary spines reminds as of 

 a similar structure in Porocidaris, figured by Thomson* in his Depths of the 

 Sea The outer granular part of the spines of this genus is formed subse- 

 quently as a tip to the basal portion, without the usual cellular sheath which 

 form- the longitudinal serrations of Echini spines. This gives us an explana- 

 tion of the apparently anomalous structure of the base of the older spine- of 

 these two genera, which appear a< if the} had been broken off and soldered 

 again. This granular addition is the homologue of a similar tip, which is found 

 in all Arbaciadae, and has been particularly well described by Desmoulins. 



It remain- alwa\s as a Mat. spathiform appendage in the shorter spine- of 

 • I ii.,m ..n. W Th Dcpthi ol thi Sen 1878, p 108, f. II. 



