PURPLE HEART-URCHIN. 185 



curved, especially those of the back, towards the anus ; 

 but the spines which thickly clothe the greater part of the 

 body are short and close-pressed, bending over each other, 

 the greater number being directed towards the posterior 

 extremity. The spines covering the post-oral space be- 

 neath, are divided into two sets by a median depression, 

 and each set bends forward from that median line. Their 

 apices are truncated and compressed, but not much 

 widened. On each side of the post-oral spinous space 

 below, there is an avenue which seems naked ; but when 

 we look closely to the surface, we find there are little 

 slender hairs scattered here and there on the surface. 

 These little hairs when magnified prove to be spines, not 

 differing in their structure from the larger spines. The 

 spines around the anus bend over it for protection, and the 

 spines within the bounds of the sub- anal impression form 

 two projecting tufts or tails. 



When we rub away all the spines, we then see the 

 structure and markings of the shell well displayed. Above 

 there is a star formed by the four lanceolate leaf-shaped 

 ambulacra. The number of pores in each of these ambu- 

 lacra, which are nearly equal in size, is about forty-eight, 

 and they are placed close together. Transverse grooves 

 run between the pairs of pores. The two anterior ambu- 

 lacra are somewhat sinous. The central is placed in a 

 shallow groove, and almost obsolete ; but when we look 

 within the shell, we see that its pores are placed pretty 

 closely together in a single row on each side of the 

 median suture, the pores of the rows alternating. In the 

 centre of all the ambulacra is a little oblong-quadrangular 

 depression, at the anterior end of which are seen the four 

 ovarian holes, the two hindermost of which are placed 

 further apart than the two foremost. The whole of the 



