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 LVIIL.) 
GEenus Encope 
E. michelini. Ambulacral 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 sPATANGOIDE 
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. 
