ECHINOMETRA. 



431 



spines of the actinal side of II. mammillatus ; the top of the flat spines is 

 usually of a darker tint, but the contrast between the pattern of coloration 

 of the spines of the lower surface and those above the ambitus is not so 

 marked. 



ECHINOMETRA. 



Echinometra Rondel, 1554, De Piscib. Mar. (Breyn.) 

 (See Part II. p. 282.) 



Echinometra lucunter 



! Cidaris lucunter Leske, 1778, Kl. Add. 

 ! Echinometra lucunter Blainv., 1834, Actin. 



PL IV. f. 4; PI. VI. f. 12; PI XXXVI. f. 1. 



This species is perhaps the most variable species in a genus remarkable 

 for the range of the specific characters. The general coloration of the spines 

 ranges from a dark violet to almost straw-color tipped with violet, or uniform 

 light pink spines tipped with yellow, and all possible gradations between 

 this and a dark violet shaft with a yellow tip, or a light green shaft shad- 

 ing into a darker point tipped with yellow or a lighter shade than the body 

 of the shaft. The milled ring is generally of a brilliant white color. The 

 principal characteristic of this species is the shortness of the arcs composing 

 the narrow poriferous zone, never having more than five pairs of pores, usu- 

 ally only four, to each arc. The outer row of ambulacral tubercles is reduced 

 to minute tubercles, not forming prominent vertical rows as in the two 

 American species, though in very large specimens (which have been called E. 

 heteropora), and correspond to a variety of our common West India species 

 which has been called E. lobata. This outer row of tubercles is more marked 

 with a tendency to separate one of the pairs of pores from the others. The co- 

 ronal plates do not greatly increase in size during growth, but increase rapidly 

 in number. In our West India species the opposite is the case. The maclre- 



