ECHIXODERMATA. 105 



teen in number, and shorter than the diameter of tlie 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 upon the lower surface. 



Order III. Ophiuroidea. 



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

 {Ophioglyplia, Ophiuraj Ophiothrix, Ophiocoma, &c.) The body in 



Fig. 65.— Ophiuroidea. Ophioglyplia lacertom : A, Outline, of the natural size: B, 

 The disc viewed from above, twice the natural size ; C, The disc viewed from 

 below, showing the mouth and genital fissures, twice the natural size. (Original.) 



the Ophiuroidea consists of a circular central disc covered with small 

 calcareous plates, and giving off five long slender arms (fig. 65), 



