78 



Zoological Society. 



The mouth is five-radiate, and placed in the centre of the under- 

 surface of the disk, in the midst of the origin of the arms ; a strong 

 osseous bar, taking the place of the interbrachial plate of the Ophiurce, 

 unites the bases of the arms, and forms a solid ring round the mouth ; 

 the five bars give origin to as many calcareous cones, which passing 



inwards nearly meet in the centre ; the intervening spaces form the 

 five-radiate mouth. Articulated to the cones are a number of spines, 

 which increase in number and length towards the apex ; behind the 

 base of the cone, in the angle of each interbrachial space, are placed 

 two genital openings ; the madreporiform tubercle also occupies the 

 angle of one of these spaces. 



