226 MARINE INVERTEBRATES 



of the posterior end. The three anterior zones are shorter than the pos- 

 terior pair. On the upper side of the disk the spines all turn toward 

 the periphery. The color of the living animal is greenish-blue. It is 

 very abundant from Cape Hatteras southward in shallow water, and the 

 shells are sometimes found as far north as Cape Cod. (Plate LVIII. ) 



GENUS Encope 



E. michelini. Ambulaeral zones unequal in size, the posterior pair 

 usually longer than the others ; lunales like notches in the margin, with 

 a large one opening between the posterior ambulacral zones nearly 

 in the center of the disk ; disk rounded in front and square at the back. 

 Common on the coasts of southern Florida and the Gulf of Mexico in 

 shallow water. (Plate LVIII.) 



ORDER SPATANGOIDEA 



HEART-URCHINS 



The Spatangoidea, or heart-urchins, have heart-shaped or thick 

 elliptical bodies. The mouth and excretory opening are both 

 away from the center and on the ventral side. These animals 

 seem deformed, so much are they out of symmetry and so dif- 

 ferent in outline from the other orders of the class. The am- 

 bulacral zones are in circles, or petaloid in outline, as in cake- 

 urchins, but are not continuous, and the anterior one is usually 

 unlike the others and frequently without pores. The entire body 

 is covered with spines, and these are the chief organs of locomo- 

 tion ; the greater part of them turn backward, giving the living 

 animal the semblance of a porcupine. The mouth is protected by 

 a projecting plate, but Aristotle's lantern is absent in this order. 

 The anatomy is in general the same as in the other orders, but 

 the organs are turned in conformity with the inclosing shell. 

 Most of these animals bury themselves in sand or mud and live in 

 deep water ; a few only are littoral species. 



FAMILY SPATANGOIDJE 



GENUS Moira 



M. atropos. Size about one inch by one and a half inches, and one 

 inch thick ; color yellowish-white, with brown spines. Found from 

 North Carolina to Florida, from the shore to deep water. 



