COMMON HEART-URCHIN. 191 



Echinus pusiUus, Gmelin, 3198. 



Echinus cordatus, Pennant, Brit. Zool. IV. p. 69. t. xxxiv. f. 75. 



Spatangus pusiUus, Leske, p. 230, t. xxiv. f. c, d, e, xxxviii. fig. 5. 



Spaiangus cordatus, Fleming, Brit. An. p. 480. 



Spatangus flavescens, Muller, Zool. Dan. III. t. xci. f. 1-4. 



Spatangus arcuarius, Lam. 1 Edit. III. p. 31 ; 2 Edit. III. p. 328. Blainv. 



Man. d'Actin. p. 201. 

 Amphidotus pusiUus, Agassiz, Prod. 



The commonest of all the Heart-Urchins is the species 

 before ns, found throughout the seas of Europe. It 

 abounds in all our sandy bays, and after storms great num- 

 bers are cast on shore. Popularly it is known by the 

 names of MermaidVhead, ChildVhead Urchin, and Hairy 

 Sea-egg. In form it is broadly heart-shaped ; dorsally, 

 the centre is much depressed, and a deep groove with pre- 

 cipitous sides runs from the ovarian holes to near the 

 mouth. This depression and part of the groove are 

 bounded by the ovate dorsal impression from which and 

 beyond radiate the four ambulacra, which are placed also 

 in grooves, though not so deep as the centre. These am- 

 bulacra are very wide at their origins, and taper towards 

 their centres, when each row of pores runs on parallel, and 

 is truncate at the extremity. The numbers of pores in 

 the anterior pair are generally six and eleven in each, in 

 the posterior nine and nine. The two anterior ovarian 

 holes approximate, the two posterior diverge. Above the 

 anus the back is exceedingly prominent, much higher than 

 any other part of the body. The anus itself is almost 

 round. It is formed of a number of small triangular hair- 

 like plates radiating to a centre. These are surrounded 

 by an ovate ring of eleven small polygonal plates, and 

 these again are bounded below by five quadrangular plates, 

 the lowermost of which are very large. The post-anal 

 impression is somewhat lenticular in form. Beneath, the 



