ECHINODEEMATA. 



105 



teen in number, and shorter than the diameter of the disc. In the 

 Cushion-stars (Goniaster) the body is in the form of a five-angled 

 disc, more or less flattened on both sides, the rays being only 

 marked out by the ambulacral grooves vipon the lower surface. 



Order III. Ophiuroidea. 



This order comprises the common Brittle-stars and Sand-stars 

 {Ophioglypha, Ophiura, Ophiothrix, Opluocoma, &c.) The body in 



Fig. fi5.— Opliiurniilcn. Ophii^dhjflw, lacertosa : A, Outline, of tlie iiutural size; B, 

 Tlic liiso \'ieweil froiri al>ove, twice tlie n.ituial size ; C, Tlie dise liewed from 

 below, showing the mouth and yenital lissmx-s, twieo the natural size. ((Jriginal.) 



the Ophiuroidea consists of a circular central disc covei'ed with small 

 calcareous plates, and giving olf five long .slender arms (fig. 6.5), 



