OPHirROIDEA FKOM THE KOREIIT SEAS, 



463 



the mouth, and is bounded by the ridge of the generative slit on 

 either side ; and this is very minutely spined, the row of spines 

 meeting close to the mouth-shield. 



The mouth-shields are small, slightly longer than broad, cordi- 

 form, angular within, and curved broadly without, the madreporic 

 being rounder in outline. They arc remote from the margin of 

 the disk, and are attached aborally to the process of the conver- 

 ging generative slits. The side mouth-shields are rather large, 

 bound much of the mouth-shield, are narrow and united at their 

 inner edge, and rather broad and triangular near the lower arm- 

 plate. 



The jaws are short, and together they form almost a semi- 

 circle, instead of an angle, and are broader than long. There are 

 eleven mouth-papilloe to eacli angle ; the last but one, externally, is 

 the largest, and tliat at the angle resembles a small true tooth ; 

 those on either side project, but are rather blunt. The teeth are 

 broad, and rather square at the free edge, and are five in 

 number. 



The under arm-plates vary slightly in shape, and those in mid 

 arm are very broad aborally, rather angular within, but still, on 

 the whole, are longer than broad. Tliere is a slight curve ab- 

 orally, where the plate forms not only the under arm, but en- 

 croaches on either side : there is a re-entering curve on either 

 side for the tentacle, and then the sides slope sharply inwards, 

 and the oral edge is short and approaches a point, or the oral 

 portion of the plate may present a sharp and narrow curve. 



The side arm-plates encroach by a blunt process upon the under 

 surface, and produce the angularity of the under plates, but they 

 do not separate them entirely. 



The upper arm-plates overlap, are broader than long, and have 

 a broad curve aborally and a faint longitudinal ridge ; they are 

 conTex from side to side, .broadest and least curved within, and 

 the sides slope inwards from the oral edge. There is an accessory 

 plate on each side, and it is broader and curved without and 

 angular within, being close to the side of the upper arm-plate, 

 and not projecting beyond its bold distal curve. 



The side arm-plate has a narrow process which reaches slightly 

 towards the median line beyond the accessory piece, which is 

 pretty constant to the tip of the arm. The side arm-plates are 

 small, form much of the side of the arm ; they are rather thick, 

 project slightly from the arm, and their free edge, which supports 



