ECHINODERMATA 75 



stout, and very closely set. The test is also much stronger 

 than in the foregoing. It is somewhat depressed in form, 

 and is about five or six inches in diameter. In colour it is 

 usually of a deep and regular purple, but I have had speci- 

 mens that were pure white. 



It rejoices, in the books that have references to it, in no 



Fig. 30. Echinus lividus. f Natural size 



less than sixteen names, but I have given what seems to be 

 the one first applied to it. It lives in rocky situations at 

 low- tide limit, but is sometimes taken in dredge and trawl 

 when these have worked in stony ground. It is the test of 

 one of these which is shown in Fig. 28. 



The Heart-shaped Urchins differ in various respects 

 from the foregoing, chief of which is their outward form. 



They are roughly triangular and more or less flattened. 



