VIII ECHINODEBMATA -SYSTEMATIC REVIEJV 293 



the shell is very flat : ScutcUa (Fig. 234), Echinodiscus, Encopc, MoJUta (Fig. 235), 

 Rotula, Arachnoid"s, etc. (extant and fossil). 



Fig. -235.— Mellita testudinata? Ironi the oral side (driginul). 



Order 5. Spatangoida. 



Month central, snb-central, or on the anterior edge of the oral surface of the test 

 Anus outside the apical system, in tlie posterior interradins. External gills, jaws, 

 teeth, and perignathous apophysial ring wanting. Spha^ridia present. The ambu- 

 lacra generally form apical petaloids. The test is bilaterally symmetrical, arched, 

 often heart-shaped. 



Sub-Order 1. Cassiduloidea. 



Fam. 1. Echinoneidse : AV/(///'«Y>;/i<.s', Echinoneus, Oligoinjijus, EcJiinolrisstis, etc. 

 (extant and fossil). Fam. 2. Cassidulidae : Cassiduhis, C'atopygus, Chjpeus, Pygurus, 

 Echinolampas, etc. (mostly fossil). Fam. 3. CoIIyritidse : Collyritcs, JDysastcr, etc. 

 (fossil). Fam. 4. Flesiospatangidse : EoIanipKis, Archiacia, etc. (fossil). 



Sub-Order 2. Spatangoidea. 



Fam. 1. Anan-chytidse : Echinocorys, Hulasfcr, Hoiiipiteustes, CardiaMer, Urc- 

 chiiius, Oystcchiniia, (Jalymne, etc. (the last three genera extant, the rest fossil). 

 Fam. 2. Spatangidse — Group 1, Adetes : Isastcr, Echino^patiigux, Hderolampas, 

 Hemipatagu>^, etc. (almost exclusively fossil) ; Group 2, Prymnadetes : Hcniiastcr, 

 Faoriiia, Linthia, Schizaster (Fig. 236), Agassizln (extant and fossil) ; Group 3, 

 Prymnodesmia : Micraster, Brissus, Spatangomorpha, Brissopsis, Spatangus, Palceop- 

 vustcs (Fig. 237), Echinocardium, Lovcnia, etc. (extant and fossil) ; Group 4, 

 Apetala : (Jcnicopatagus, Palceobrissus, Aceste, Aei-oiK, etc. (extant and fossil). 



