[Illustration: /Echinarachnius parma/, the sand-dollar. Much smaller than natural size.] ^E. excentricus.^ This is the common sand-dollar of the Pacific coast. The disk, instead of being circular as in /E. parma/, is somewhat straight across the posterior end, and the posterior ambulacral zones are shorter than the other three. The upper side of the disk is raised, forming a cone-like elevation, the apex being the center of the figure. GENUS ^Mellita^ ^M. testudinata.^ The disk is rounded in front and straight in the back. Four long, narrow lunules, or cuts, occur on the sides in line with the ambulacral, petal-shaped zones, but do not extend quite to the edge of the disk; and a wide lunule occurs in the interambulacral space [pg226] of the posterior end. The three anterior zones are shorter than the posterior 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.^ Ambulacral zones unequal in size, the posterior pair usually longer than the others; lunules 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 different in outline from the other orders of the class. The ambulacral 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 locomotion; 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 ~SPATANGOIDÆ~ 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. [Illustration: PLATE LVIII. Clypeaster ravenellii. Mellita testudinata. Encope michelini. Test of Metalia pectoralis. Lovenia cordiformis.] [pg227] GENUS ^Lovenia^