ASPIDODIADEMA ANTILLAEUM. 25 
a remarkable and interesting type of peclicellarice, which in A. Jacohyi are 
quite large and numerous, and are found scattered over the whole of the 
abactinal part of the test, especially in the ambulacral area. These are 
sheathed pedicellarias, if I may call them so. The sliaft consists of a long, 
slender radiole, distinctly articulated, surrounded by a huge fleshy sheath, 
swelling out into three large bags on the sides, covering a little more than 
half the length of the shaft. This sheath extends from the base, where it 
covers the articulation, to the extremity of the pedicellaria3, at the tip of 
which is placed a small head enclosed within this sheath. The sheath at the 
extremity expands into a three-lobed cupuliform tip. These pedicellarite re- 
call at once the remarkable sheathed secondary spines which I have described 
in Asthenosoma Gnihei, they form an additional link in the chain, proving that 
pedicellariae are only modified spines. The diminutive heads of these pedi- 
cellariae, if completelj' resorbed, would leave us a sheathed spine identical 
with the sheathed spine of the Echinothuria? ; the existence in that family of 
club-shaped primary spines, as in Phormosoma bursaria, the tip of which is still 
sheathed to a certain extent, shows how close is the relation of the sheathed 
spines to true pedicellaria3. 
How far this sheath is analogous to the peculiar gland discovered by 
Sladeu * in some of the types of pedicellarioe, I am unable to state positively 
at present, but I am inclined to consider it as a modification of this gland. 
If this be so, the sheathed pedicellariae are only an extreme modification 
of the simple extension of the muscular system of the test over the shaft of 
the spines, and over the stem of the ordinary type of pedicellarice ; this 
extension being either modified into a sheath covering the whole of the sec- 
ondary or primary spines, or merely a part of the shaft ; or into a gland ; or 
into a sheath, such as we find it in Aspidodiadema and the Echinothurije. 
* Aspidodiadema antillarum A. Ag. 
Aspidodiadema antUlarum A. Ag. Bull. M. C. Z., VIII., No. 2, p. VS, 1880. 
Aspidodiadema microtuberculatum A. Ag. Bull. M. C. Z., V., No. 9, p. 188 (non Chall. 
Echinoidea). 
Southeast extremity of Cuba, Santa Cruz to St. Vincent. 451 to 1,568 fathoms ; most abun- 
dant between 400 and 800 fathom.s. " - 
PL IX. 
The genital ring of A. aniilhirum is comparatively larger than that of A. 
Jacobyi. The plates of the genital and ocular system are of nearly uniform 
* W. p. Sladcn, Ann. and Mag. of Nat. Hist., August, 1880. 
