ASPIDOD] V l > I :.M \ ANTILLARUM. 25 



a remarkable and interesting type of pedicellariae, which in A.Jacobyi are 

 quite large and numerous, and are found scattered over the whole of the 

 abactinal pari of the test, especially in the ambulacra! area. These are 

 sheathed pedicellariae, if I may call them so. The shafl 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 

 ciivcrs the articulation, to the extremity of the pedicellariae, 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 pedicellariae re- 

 call at once the remarkable sheathed secondary spines which I have described 

 in Asthenosoma Grubei, they form an additional link in the chain, proving that 

 pedicellariae are only modified spines. The diminutive heads <>f these pedi- 

 cellariae, if completel} resorbed, would leave us a sheathed spine identical 

 with the sheathed spine of the Echinothuriae ; 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 pedicellariae. 



How far this sheath is analogous to the peculiar gland discovered by 

 Sliiden * in some of the types of pedicellariae, 1 am unable to state positively 

 ai 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 shafl of 

 the spines, and over the stem of the ordinary type of pedicellariae; this 

 extension being either modified into a sheath covering the whole of the sec- 

 ondary or primary spine-, or merely a part of the shafl ; or into a -land ; or 

 into a sheath, Buch as we find it in Aspidodiadema and the Echinothuriae. 



* Aspidodiadema antillarum A.. A 



Aspidodiadema antillarum A. A.G. Bull. M. C. /... VTH., No 2, p 73, 1880. 

 Aspidodiadema microtuberculatum A. A.G. Bull M. < '. '/.. V., No. 9 p. 188 (non I lull. 

 Echini 

 Southeast extremity of Cuba, Santa Cruz to St. Vincent \~<\ to 1,568 fathoms ; most aban- 

 don! between WO and 800 Fathoms. 



PI IX. 



The genital ring of .1. antillarum is comparatively larger than thai of A. 



Jacobyi. The plates of the genital and ocular system are of nearly uniform 



• W. P. si. Mn,. Ann. and Mag. of Nat. BCisI ' 



