66 THE ATLANTIC. [CHAP. ii. 



enpies the centre, encircled by a row of six plates of the same 

 form ; and beyond these there is an outer row, consisting of the 

 five pairs of thick radial shields and five oblong plates, occu- 



FiG. \9.—Ophiomiisiwtn iiulchellum,yv\\u.\.-a Thomson. Oral aspect of the disk. Seven 

 times the natural size. (No. S7.) 



pying the interbrachial spaces. The month-papillse are entire- 

 ly coalesced into a continuous calcareous border ; the mouth- 

 shields are diamond-shaped, and rather small ; the side mouth- 

 shields, on the contrary, are unusually large. The first four or 

 five under arm-plates are shield-shaped, and rather large, with 

 well-marked rounded tentacle-scales ; but they suddenly become 

 small when they reach the narrow part of the arm, and the 

 tentacle-scales disappear. The side arm-plates on the proximal 



